diff --git a/mmcv/ops/psa_mask.py b/mmcv/ops/psa_mask.py
index 0786e2d25f..45f4946662 100644
--- a/mmcv/ops/psa_mask.py
+++ b/mmcv/ops/psa_mask.py
@@ -1,4 +1,7 @@
 # Modified from https://github.com/hszhao/semseg/blob/master/lib/psa
+from typing import Optional, Tuple
+
+import torch
 from torch import nn
 from torch.autograd import Function
 from torch.nn.modules.utils import _pair
@@ -20,7 +23,8 @@ def symbolic(g, input, psa_type, mask_size):
             mask_size_i=mask_size)
 
     @staticmethod
-    def forward(ctx, input, psa_type, mask_size):
+    def forward(ctx, input: torch.Tensor, psa_type: str,
+                mask_size: int) -> torch.Tensor:
         ctx.psa_type = psa_type
         ctx.mask_size = _pair(mask_size)
         ctx.save_for_backward(input)
@@ -45,7 +49,9 @@ def forward(ctx, input, psa_type, mask_size):
         return output
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(
+            ctx, grad_output: torch.Tensor
+    ) -> Tuple[torch.Tensor, None, None, None]:
         input = ctx.saved_tensors[0]
         psa_type = ctx.psa_type
         h_mask, w_mask = ctx.mask_size
@@ -71,7 +77,7 @@ def backward(ctx, grad_output):
 
 class PSAMask(nn.Module):
 
-    def __init__(self, psa_type, mask_size=None):
+    def __init__(self, psa_type: str, mask_size: Optional[tuple] = None):
         super().__init__()
         assert psa_type in ['collect', 'distribute']
         if psa_type == 'collect':
@@ -82,7 +88,7 @@ def __init__(self, psa_type, mask_size=None):
         self.mask_size = mask_size
         self.psa_type = psa_type
 
-    def forward(self, input):
+    def forward(self, input: torch.Tensor) -> torch.Tensor:
         return psa_mask(input, self.psa_type_enum, self.mask_size)
 
     def __repr__(self):
diff --git a/mmcv/ops/riroi_align_rotated.py b/mmcv/ops/riroi_align_rotated.py
index af1e6098e4..1de810cc5f 100644
--- a/mmcv/ops/riroi_align_rotated.py
+++ b/mmcv/ops/riroi_align_rotated.py
@@ -1,4 +1,7 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any, Optional, Tuple, Union
+
+import torch
 import torch.nn as nn
 from torch.autograd import Function
 
@@ -11,14 +14,14 @@
 class RiRoIAlignRotatedFunction(Function):
 
     @staticmethod
-    def forward(ctx,
-                features,
-                rois,
-                out_size,
-                spatial_scale,
-                num_samples=0,
-                num_orientations=8,
-                clockwise=False):
+    def forward(ctx: Any,
+                features: torch.Tensor,
+                rois: torch.Tensor,
+                out_size: Union[int, tuple],
+                spatial_scale: float,
+                num_samples: int = 0,
+                num_orientations: int = 8,
+                clockwise: bool = False) -> torch.Tensor:
         if isinstance(out_size, int):
             out_h = out_size
             out_w = out_size
@@ -54,7 +57,9 @@ def forward(ctx,
         return output
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(
+        ctx: Any, grad_output: torch.Tensor
+    ) -> Optional[Tuple[torch.Tensor, None, None, None, None, None, None]]:
         feature_size = ctx.feature_size
         spatial_scale = ctx.spatial_scale
         num_orientations = ctx.num_orientations
@@ -67,7 +72,7 @@ def backward(ctx, grad_output):
         out_w = grad_output.size(3)
         out_h = grad_output.size(2)
 
-        grad_input = grad_rois = None
+        grad_input = None
 
         if ctx.needs_input_grad[0]:
             grad_input = rois.new_zeros(batch_size, num_channels, feature_h,
@@ -83,7 +88,8 @@ def backward(ctx, grad_output):
                 num_orientations=num_orientations,
                 clockwise=clockwise)
 
-            return grad_input, grad_rois, None, None, None, None, None
+            return grad_input, None, None, None, None, None, None
+        return None
 
 
 riroi_align_rotated = RiRoIAlignRotatedFunction.apply
@@ -111,11 +117,11 @@ class RiRoIAlignRotated(nn.Module):
     """
 
     def __init__(self,
-                 out_size,
-                 spatial_scale,
-                 num_samples=0,
-                 num_orientations=8,
-                 clockwise=False):
+                 out_size: tuple,
+                 spatial_scale: float,
+                 num_samples: int = 0,
+                 num_orientations: int = 8,
+                 clockwise: bool = False):
         super().__init__()
 
         self.out_size = out_size
@@ -124,7 +130,8 @@ def __init__(self,
         self.num_orientations = int(num_orientations)
         self.clockwise = clockwise
 
-    def forward(self, features, rois):
+    def forward(self, features: torch.Tensor,
+                rois: torch.Tensor) -> torch.Tensor:
         return RiRoIAlignRotatedFunction.apply(features, rois, self.out_size,
                                                self.spatial_scale,
                                                self.num_samples,
diff --git a/mmcv/ops/roi_align.py b/mmcv/ops/roi_align.py
index 7e387f944b..ca802f60cd 100644
--- a/mmcv/ops/roi_align.py
+++ b/mmcv/ops/roi_align.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any
+
 import torch
 import torch.nn as nn
 from torch.autograd import Function
@@ -62,14 +64,14 @@ def symbolic(g, input, rois, output_size, spatial_scale, sampling_ratio,
                 mode_s=pool_mode)
 
     @staticmethod
-    def forward(ctx,
-                input,
-                rois,
-                output_size,
-                spatial_scale=1.0,
-                sampling_ratio=0,
-                pool_mode='avg',
-                aligned=True):
+    def forward(ctx: Any,
+                input: torch.Tensor,
+                rois: torch.Tensor,
+                output_size: int,
+                spatial_scale: float = 1.0,
+                sampling_ratio: int = 0,
+                pool_mode: str = 'avg',
+                aligned: bool = True) -> torch.Tensor:
         ctx.output_size = _pair(output_size)
         ctx.spatial_scale = spatial_scale
         ctx.sampling_ratio = sampling_ratio
@@ -108,7 +110,7 @@ def forward(ctx,
 
     @staticmethod
     @once_differentiable
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         rois, argmax_y, argmax_x = ctx.saved_tensors
         grad_input = grad_output.new_zeros(ctx.input_shape)
         # complex head architecture may cause grad_output uncontiguous.
@@ -175,12 +177,12 @@ class RoIAlign(nn.Module):
         },
         cls_name='RoIAlign')
     def __init__(self,
-                 output_size,
-                 spatial_scale=1.0,
-                 sampling_ratio=0,
-                 pool_mode='avg',
-                 aligned=True,
-                 use_torchvision=False):
+                 output_size: tuple,
+                 spatial_scale: float = 1.0,
+                 sampling_ratio: int = 0,
+                 pool_mode: str = 'avg',
+                 aligned: bool = True,
+                 use_torchvision: bool = False):
         super().__init__()
 
         self.output_size = _pair(output_size)
@@ -190,7 +192,7 @@ def __init__(self,
         self.aligned = aligned
         self.use_torchvision = use_torchvision
 
-    def forward(self, input, rois):
+    def forward(self, input: torch.Tensor, rois: torch.Tensor) -> torch.Tensor:
         """
         Args:
             input: NCHW images
diff --git a/mmcv/ops/roi_align_rotated.py b/mmcv/ops/roi_align_rotated.py
index 8551b172b5..f970ef4d8a 100644
--- a/mmcv/ops/roi_align_rotated.py
+++ b/mmcv/ops/roi_align_rotated.py
@@ -1,4 +1,7 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any, Optional, Tuple, Union
+
+import torch
 import torch.nn as nn
 from torch.autograd import Function
 from torch.nn.modules.utils import _pair
@@ -37,14 +40,14 @@ def symbolic(g, input, rois, output_size, spatial_scale, sampling_ratio,
             clockwise_i=clockwise)
 
     @staticmethod
-    def forward(ctx,
-                input,
-                rois,
-                output_size,
-                spatial_scale,
-                sampling_ratio=0,
-                aligned=True,
-                clockwise=False):
+    def forward(ctx: Any,
+                input: torch.Tensor,
+                rois: torch.Tensor,
+                output_size: Union[int, tuple],
+                spatial_scale: float,
+                sampling_ratio: int = 0,
+                aligned: bool = True,
+                clockwise: bool = False) -> torch.Tensor:
         ctx.output_size = _pair(output_size)
         ctx.spatial_scale = spatial_scale
         ctx.sampling_ratio = sampling_ratio
@@ -71,7 +74,10 @@ def forward(ctx,
         return output
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(
+        ctx: Any, grad_output: torch.Tensor
+    ) -> Tuple[Optional[torch.Tensor], Optional[torch.Tensor], None, None,
+               None, None, None]:
         feature_size = ctx.feature_size
         rois = ctx.saved_tensors[0]
         assert feature_size is not None
@@ -151,11 +157,11 @@ class RoIAlignRotated(nn.Module):
         },
         cls_name='RoIAlignRotated')
     def __init__(self,
-                 output_size,
-                 spatial_scale,
-                 sampling_ratio=0,
-                 aligned=True,
-                 clockwise=False):
+                 output_size: Union[int, tuple],
+                 spatial_scale: float,
+                 sampling_ratio: int = 0,
+                 aligned: bool = True,
+                 clockwise: bool = False):
         super().__init__()
 
         self.output_size = _pair(output_size)
@@ -164,7 +170,7 @@ def __init__(self,
         self.aligned = aligned
         self.clockwise = clockwise
 
-    def forward(self, input, rois):
+    def forward(self, input: torch.Tensor, rois: torch.Tensor) -> torch.Tensor:
         return RoIAlignRotatedFunction.apply(input, rois, self.output_size,
                                              self.spatial_scale,
                                              self.sampling_ratio, self.aligned,
diff --git a/mmcv/ops/roi_pool.py b/mmcv/ops/roi_pool.py
index f63faabb46..e295b6a0c1 100644
--- a/mmcv/ops/roi_pool.py
+++ b/mmcv/ops/roi_pool.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any, Tuple, Union
+
 import torch
 import torch.nn as nn
 from torch.autograd import Function
@@ -23,7 +25,11 @@ def symbolic(g, input, rois, output_size, spatial_scale):
             spatial_scale_f=spatial_scale)
 
     @staticmethod
-    def forward(ctx, input, rois, output_size, spatial_scale=1.0):
+    def forward(ctx: Any,
+                input: torch.Tensor,
+                rois: torch.Tensor,
+                output_size: Union[int, tuple],
+                spatial_scale: float = 1.0) -> torch.Tensor:
         ctx.output_size = _pair(output_size)
         ctx.spatial_scale = spatial_scale
         ctx.input_shape = input.size()
@@ -49,7 +55,9 @@ def forward(ctx, input, rois, output_size, spatial_scale=1.0):
 
     @staticmethod
     @once_differentiable
-    def backward(ctx, grad_output):
+    def backward(
+            ctx: Any, grad_output: torch.Tensor
+    ) -> Tuple[torch.Tensor, None, None, None]:
         rois, argmax = ctx.saved_tensors
         grad_input = grad_output.new_zeros(ctx.input_shape)
 
@@ -70,13 +78,15 @@ def backward(ctx, grad_output):
 
 class RoIPool(nn.Module):
 
-    def __init__(self, output_size, spatial_scale=1.0):
+    def __init__(self,
+                 output_size: Union[int, tuple],
+                 spatial_scale: float = 1.0):
         super().__init__()
 
         self.output_size = _pair(output_size)
         self.spatial_scale = float(spatial_scale)
 
-    def forward(self, input, rois):
+    def forward(self, input: torch.Tensor, rois: torch.Tensor) -> torch.Tensor:
         return roi_pool(input, rois, self.output_size, self.spatial_scale)
 
     def __repr__(self):
diff --git a/mmcv/ops/roiaware_pool3d.py b/mmcv/ops/roiaware_pool3d.py
index 2096b436f0..9a09049b55 100644
--- a/mmcv/ops/roiaware_pool3d.py
+++ b/mmcv/ops/roiaware_pool3d.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any, Tuple, Union
+
 import torch
 from torch import nn as nn
 from torch.autograd import Function
@@ -25,7 +27,10 @@ class RoIAwarePool3d(nn.Module):
             Default: 'max'.
     """
 
-    def __init__(self, out_size, max_pts_per_voxel=128, mode='max'):
+    def __init__(self,
+                 out_size: Union[int, tuple],
+                 max_pts_per_voxel: int = 128,
+                 mode: str = 'max'):
         super().__init__()
 
         self.out_size = out_size
@@ -34,7 +39,8 @@ def __init__(self, out_size, max_pts_per_voxel=128, mode='max'):
         pool_mapping = {'max': 0, 'avg': 1}
         self.mode = pool_mapping[mode]
 
-    def forward(self, rois, pts, pts_feature):
+    def forward(self, rois: torch.Tensor, pts: torch.Tensor,
+                pts_feature: torch.Tensor) -> torch.Tensor:
         """
         Args:
             rois (torch.Tensor): [N, 7], in LiDAR coordinate,
@@ -55,8 +61,9 @@ def forward(self, rois, pts, pts_feature):
 class RoIAwarePool3dFunction(Function):
 
     @staticmethod
-    def forward(ctx, rois, pts, pts_feature, out_size, max_pts_per_voxel,
-                mode):
+    def forward(ctx: Any, rois: torch.Tensor, pts: torch.Tensor,
+                pts_feature: torch.Tensor, out_size: Union[int, tuple],
+                max_pts_per_voxel: int, mode: int) -> torch.Tensor:
         """
         Args:
             rois (torch.Tensor): [N, 7], in LiDAR coordinate,
@@ -108,7 +115,9 @@ def forward(ctx, rois, pts, pts_feature, out_size, max_pts_per_voxel,
         return pooled_features
 
     @staticmethod
-    def backward(ctx, grad_out):
+    def backward(
+        ctx: Any, grad_out: torch.Tensor
+    ) -> Tuple[None, None, torch.Tensor, None, None, None]:
         ret = ctx.roiaware_pool3d_for_backward
         pts_idx_of_voxels, argmax, mode, num_pts, num_channels = ret
 
diff --git a/mmcv/ops/roipoint_pool3d.py b/mmcv/ops/roipoint_pool3d.py
index 2a9315bd99..3c16f5fa67 100644
--- a/mmcv/ops/roipoint_pool3d.py
+++ b/mmcv/ops/roipoint_pool3d.py
@@ -1,3 +1,6 @@
+from typing import Any, Tuple
+
+import torch
 from torch import nn as nn
 from torch.autograd import Function
 
@@ -17,11 +20,12 @@ class RoIPointPool3d(nn.Module):
             Default: 512.
     """
 
-    def __init__(self, num_sampled_points=512):
+    def __init__(self, num_sampled_points: int = 512):
         super().__init__()
         self.num_sampled_points = num_sampled_points
 
-    def forward(self, points, point_features, boxes3d):
+    def forward(self, points: torch.Tensor, point_features: torch.Tensor,
+                boxes3d: torch.Tensor) -> Tuple[torch.Tensor]:
         """
         Args:
             points (torch.Tensor): Input points whose shape is (B, N, C).
@@ -41,7 +45,13 @@ def forward(self, points, point_features, boxes3d):
 class RoIPointPool3dFunction(Function):
 
     @staticmethod
-    def forward(ctx, points, point_features, boxes3d, num_sampled_points=512):
+    def forward(
+            ctx: Any,
+            points: torch.Tensor,
+            point_features: torch.Tensor,
+            boxes3d: torch.Tensor,
+            num_sampled_points: int = 512
+    ) -> Tuple[torch.Tensor, torch.Tensor]:
         """
         Args:
             points (torch.Tensor): Input points whose shape is (B, N, C).
@@ -73,5 +83,5 @@ def forward(ctx, points, point_features, boxes3d, num_sampled_points=512):
         return pooled_features, pooled_empty_flag
 
     @staticmethod
-    def backward(ctx, grad_out):
+    def backward(ctx: Any, grad_out: torch.Tensor) -> torch.Tensor:
         raise NotImplementedError
diff --git a/mmcv/ops/rotated_feature_align.py b/mmcv/ops/rotated_feature_align.py
index 95353b70e3..7d5954ddf2 100644
--- a/mmcv/ops/rotated_feature_align.py
+++ b/mmcv/ops/rotated_feature_align.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any
+
 import torch
 from torch.autograd import Function
 from torch.autograd.function import once_differentiable
@@ -31,7 +33,8 @@ def symbolic(g, features, best_rbboxes, spatial_scale, points):
             points_i=points)
 
     @staticmethod
-    def forward(ctx, features, best_rbboxes, spatial_scale, points):
+    def forward(ctx: Any, features: torch.Tensor, best_rbboxes: torch.Tensor,
+                spatial_scale: float, points: int) -> torch.Tensor:
         """
         Args:
             features (torch.Tensor): Input features with shape [N,C,H,W].
@@ -60,7 +63,7 @@ def forward(ctx, features, best_rbboxes, spatial_scale, points):
 
     @staticmethod
     @once_differentiable
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         """
         Args:
             grad_output (torch.Tensor): The gradiant of output features
@@ -84,9 +87,9 @@ def backward(ctx, grad_output):
         return grad_input, None, None, None
 
 
-def rotated_feature_align(features,
-                          best_rbboxes,
-                          spatial_scale=1 / 8,
-                          points=1):
+def rotated_feature_align(features: torch.Tensor,
+                          best_rbboxes: torch.Tensor,
+                          spatial_scale: float = 1 / 8,
+                          points: int = 1) -> torch.Tensor:
     return RotatedFeatureAlignFunction.apply(features, best_rbboxes,
                                              spatial_scale, points)
diff --git a/mmcv/ops/scatter_points.py b/mmcv/ops/scatter_points.py
index f8a4a5565a..5d881bfe63 100644
--- a/mmcv/ops/scatter_points.py
+++ b/mmcv/ops/scatter_points.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any, List, Optional, Tuple
+
 import torch
 import torch.nn.functional as F
 from torch import nn
@@ -14,7 +16,10 @@
 class _DynamicScatter(Function):
 
     @staticmethod
-    def forward(ctx, feats, coors, reduce_type='max'):
+    def forward(ctx: Any,
+                feats: torch.Tensor,
+                coors: torch.Tensor,
+                reduce_type: str = 'max') -> Tuple[torch.Tensor, torch.Tensor]:
         """convert kitti points(N, >=3) to voxels.
 
         Args:
@@ -42,7 +47,9 @@ def forward(ctx, feats, coors, reduce_type='max'):
         return voxel_feats, voxel_coors
 
     @staticmethod
-    def backward(ctx, grad_voxel_feats, grad_voxel_coors=None):
+    def backward(ctx: Any,
+                 grad_voxel_feats: torch.Tensor,
+                 grad_voxel_coors: Optional[torch.Tensor] = None) -> tuple:
         (feats, voxel_feats, point2voxel_map,
          voxel_points_count) = ctx.saved_tensors
         grad_feats = torch.zeros_like(feats)
@@ -73,14 +80,17 @@ class DynamicScatter(nn.Module):
             into voxel.
     """
 
-    def __init__(self, voxel_size, point_cloud_range, average_points: bool):
+    def __init__(self, voxel_size: List, point_cloud_range: List,
+                 average_points: bool):
         super().__init__()
 
         self.voxel_size = voxel_size
         self.point_cloud_range = point_cloud_range
         self.average_points = average_points
 
-    def forward_single(self, points, coors):
+    def forward_single(
+            self, points: torch.Tensor,
+            coors: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
         """Scatters points into voxels.
 
         Args:
@@ -97,7 +107,8 @@ def forward_single(self, points, coors):
         reduce = 'mean' if self.average_points else 'max'
         return dynamic_scatter(points.contiguous(), coors.contiguous(), reduce)
 
-    def forward(self, points, coors):
+    def forward(self, points: torch.Tensor,
+                coors: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
         """Scatters points/features into voxels.
 
         Args:
diff --git a/mmcv/ops/sparse_functional.py b/mmcv/ops/sparse_functional.py
index aef4320d84..5a80a545aa 100644
--- a/mmcv/ops/sparse_functional.py
+++ b/mmcv/ops/sparse_functional.py
@@ -11,7 +11,9 @@
 # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 # See the License for the specific language governing permissions and
 # limitations under the License.
+from typing import Any
 
+import torch
 from torch.autograd import Function
 
 from . import sparse_ops as ops
@@ -25,8 +27,9 @@ class SparseConvFunction(Function):
     """
 
     @staticmethod
-    def forward(ctx, features, filters, indice_pairs, indice_pair_num,
-                num_activate_out):
+    def forward(ctx: Any, features: torch.Tensor, filters: torch.nn.Parameter,
+                indice_pairs: torch.Tensor, indice_pair_num: torch.Tensor,
+                num_activate_out: torch.Tensor) -> torch.Tensor:
         """
         Args:
             features (torch.Tensor): Features that needs to convolute.
@@ -44,7 +47,7 @@ def forward(ctx, features, filters, indice_pairs, indice_pair_num,
                                indice_pair_num, num_activate_out, False)
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         indice_pairs, indice_pair_num, features, filters = ctx.saved_tensors
         input_bp, filters_bp = ops.indice_conv_backward(
             features, filters, grad_output, indice_pairs, indice_pair_num,
@@ -56,8 +59,9 @@ def backward(ctx, grad_output):
 class SparseInverseConvFunction(Function):
 
     @staticmethod
-    def forward(ctx, features, filters, indice_pairs, indice_pair_num,
-                num_activate_out):
+    def forward(ctx: Any, features: torch.Tensor, filters: torch.nn.Parameter,
+                indice_pairs: torch.Tensor, indice_pair_num: torch.Tensor,
+                num_activate_out: torch.Tensor) -> torch.Tensor:
         """
         Args:
             features (torch.Tensor): Features that needs to convolute.
@@ -75,7 +79,7 @@ def forward(ctx, features, filters, indice_pairs, indice_pair_num,
                                indice_pair_num, num_activate_out, True, False)
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         indice_pairs, indice_pair_num, features, filters = ctx.saved_tensors
         input_bp, filters_bp = ops.indice_conv_backward(
             features, filters, grad_output, indice_pairs, indice_pair_num,
@@ -87,8 +91,9 @@ def backward(ctx, grad_output):
 class SubMConvFunction(Function):
 
     @staticmethod
-    def forward(ctx, features, filters, indice_pairs, indice_pair_num,
-                num_activate_out):
+    def forward(ctx: Any, features: torch.Tensor, filters: torch.nn.Parameter,
+                indice_pairs: torch.Tensor, indice_pair_num: torch.Tensor,
+                num_activate_out: torch.Tensor) -> torch.Tensor:
         """
         Args:
             features (torch.Tensor): Features that needs to convolute.
@@ -106,7 +111,7 @@ def forward(ctx, features, filters, indice_pairs, indice_pair_num,
                                indice_pair_num, num_activate_out, False, True)
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         indice_pairs, indice_pair_num, features, filters = ctx.saved_tensors
         input_bp, filters_bp = ops.indice_conv_backward(
             features, filters, grad_output, indice_pairs, indice_pair_num,
@@ -118,8 +123,9 @@ def backward(ctx, grad_output):
 class SparseMaxPoolFunction(Function):
 
     @staticmethod
-    def forward(ctx, features, indice_pairs, indice_pair_num,
-                num_activate_out):
+    def forward(ctx, features: torch.Tensor, indice_pairs: torch.Tensor,
+                indice_pair_num: torch.Tensor,
+                num_activate_out: torch.Tensor) -> torch.Tensor:
         """
         Args:
             features (torch.Tensor): Features that needs to convolute.
@@ -137,7 +143,7 @@ def forward(ctx, features, indice_pairs, indice_pair_num,
         return out
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         indice_pairs, indice_pair_num, features, out = ctx.saved_tensors
         input_bp = ops.indice_maxpool_backward(features, out, grad_output,
                                                indice_pairs, indice_pair_num)
diff --git a/mmcv/ops/sparse_modules.py b/mmcv/ops/sparse_modules.py
index a721b30e5a..20a92aa279 100644
--- a/mmcv/ops/sparse_modules.py
+++ b/mmcv/ops/sparse_modules.py
@@ -13,6 +13,7 @@
 # limitations under the License.
 import sys
 from collections import OrderedDict
+from typing import Any, List, Optional, Union
 
 import torch
 from torch import nn
@@ -20,17 +21,18 @@
 from .sparse_structure import SparseConvTensor
 
 
-def is_spconv_module(module):
+def is_spconv_module(module: nn.Module) -> bool:
     spconv_modules = (SparseModule, )
     return isinstance(module, spconv_modules)
 
 
-def is_sparse_conv(module):
+def is_sparse_conv(module: nn.Module) -> bool:
     from .sparse_conv import SparseConvolution
     return isinstance(module, SparseConvolution)
 
 
-def _mean_update(vals, m_vals, t):
+def _mean_update(vals: Union[int, List], m_vals: Union[int, List],
+                 t: float) -> List:
     outputs = []
     if not isinstance(vals, list):
         vals = [vals]
@@ -101,7 +103,7 @@ def __init__(self, *args, **kwargs):
             self.add_module(name, module)
         self._sparity_dict = {}
 
-    def __getitem__(self, idx):
+    def __getitem__(self, idx: int) -> torch.Tensor:
         if not (-len(self) <= idx < len(self)):
             raise IndexError(f'index {idx} is out of range')
         if idx < 0:
@@ -118,14 +120,14 @@ def __len__(self):
     def sparity_dict(self):
         return self._sparity_dict
 
-    def add(self, module, name=None):
+    def add(self, module: Any, name: Optional[str] = None) -> None:
         if name is None:
             name = str(len(self._modules))
             if name in self._modules:
                 raise KeyError('name exists')
         self.add_module(name, module)
 
-    def forward(self, input):
+    def forward(self, input: torch.Tensor) -> torch.Tensor:
         for k, module in self._modules.items():
             if is_spconv_module(module):
                 assert isinstance(input, SparseConvTensor)
diff --git a/mmcv/ops/sparse_structure.py b/mmcv/ops/sparse_structure.py
index 82d04167cc..83907ab556 100644
--- a/mmcv/ops/sparse_structure.py
+++ b/mmcv/ops/sparse_structure.py
@@ -1,8 +1,11 @@
+from typing import List, Optional, Tuple, Union
+
 import numpy as np
 import torch
 
 
-def scatter_nd(indices, updates, shape):
+def scatter_nd(indices: torch.Tensor, updates: torch.Tensor,
+               shape: torch.Tensor) -> torch.Tensor:
     """pytorch edition of tensorflow scatter_nd.
 
     this function don't contain except handle code. so use this carefully when
@@ -21,18 +24,18 @@ def scatter_nd(indices, updates, shape):
 class SparseConvTensor:
 
     def __init__(self,
-                 features,
-                 indices,
-                 spatial_shape,
-                 batch_size,
-                 grid=None):
+                 features: torch.Tensor,
+                 indices: torch.Tensor,
+                 spatial_shape: Union[List, Tuple],
+                 batch_size: int,
+                 grid: Optional[torch.Tensor] = None):
         self.features = features
         self.indices = indices
         if self.indices.dtype != torch.int32:
             self.indices.int()
         self.spatial_shape = spatial_shape
         self.batch_size = batch_size
-        self.indice_dict = {}
+        self.indice_dict: dict = {}
         self.grid = grid
 
     @property
@@ -46,7 +49,7 @@ def find_indice_pair(self, key):
             return self.indice_dict[key]
         return None
 
-    def dense(self, channels_first=True):
+    def dense(self, channels_first: bool = True) -> torch.Tensor:
         output_shape = [self.batch_size] + list(
             self.spatial_shape) + [self.features.shape[1]]
         res = scatter_nd(self.indices.long(), self.features, output_shape)
diff --git a/mmcv/ops/sync_bn.py b/mmcv/ops/sync_bn.py
index e24ecb1a0a..ce8727cb37 100644
--- a/mmcv/ops/sync_bn.py
+++ b/mmcv/ops/sync_bn.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Optional
+
 import torch
 import torch.distributed as dist
 import torch.nn.functional as F
@@ -35,8 +37,10 @@ def symbolic(g, input, running_mean, running_var, weight, bias, momentum,
             stats_mode=stats_mode)
 
     @staticmethod
-    def forward(self, input, running_mean, running_var, weight, bias, momentum,
-                eps, group, group_size, stats_mode):
+    def forward(self, input: torch.Tensor, running_mean: torch.Tensor,
+                running_var: torch.Tensor, weight: torch.Tensor,
+                bias: torch.Tensor, momentum: float, eps: float, group: int,
+                group_size: int, stats_mode: str) -> torch.Tensor:
         self.momentum = momentum
         self.eps = eps
         self.group = group
@@ -126,7 +130,7 @@ def forward(self, input, running_mean, running_var, weight, bias, momentum,
 
     @staticmethod
     @once_differentiable
-    def backward(self, grad_output):
+    def backward(self, grad_output: torch.Tensor) -> tuple:
         norm, std, weight = self.saved_tensors
         grad_weight = torch.zeros_like(weight)
         grad_bias = torch.zeros_like(weight)
@@ -191,13 +195,13 @@ class SyncBatchNorm(Module):
     """
 
     def __init__(self,
-                 num_features,
-                 eps=1e-5,
-                 momentum=0.1,
-                 affine=True,
-                 track_running_stats=True,
-                 group=None,
-                 stats_mode='default'):
+                 num_features: int,
+                 eps: float = 1e-5,
+                 momentum: float = 0.1,
+                 affine: bool = True,
+                 track_running_stats: bool = True,
+                 group: Optional[int] = None,
+                 stats_mode: str = 'default'):
         super().__init__()
         self.num_features = num_features
         self.eps = eps
@@ -239,7 +243,7 @@ def reset_parameters(self):
             self.weight.data.uniform_()  # pytorch use ones_()
             self.bias.data.zero_()
 
-    def forward(self, input):
+    def forward(self, input: torch.Tensor) -> torch.Tensor:
         if input.dim() < 2:
             raise ValueError(
                 f'expected at least 2D input, got {input.dim()}D input')
diff --git a/mmcv/ops/three_interpolate.py b/mmcv/ops/three_interpolate.py
index 7256e91f6f..12b2f7611e 100644
--- a/mmcv/ops/three_interpolate.py
+++ b/mmcv/ops/three_interpolate.py
@@ -1,4 +1,4 @@
-from typing import Tuple
+from typing import Any, Tuple
 
 import torch
 from torch.autograd import Function
@@ -17,7 +17,7 @@ class ThreeInterpolate(Function):
     """
 
     @staticmethod
-    def forward(ctx, features: torch.Tensor, indices: torch.Tensor,
+    def forward(ctx: Any, features: torch.Tensor, indices: torch.Tensor,
                 weight: torch.Tensor) -> torch.Tensor:
         """
         Args:
diff --git a/mmcv/ops/three_nn.py b/mmcv/ops/three_nn.py
index 25d60bb26c..7893c8363b 100644
--- a/mmcv/ops/three_nn.py
+++ b/mmcv/ops/three_nn.py
@@ -1,4 +1,4 @@
-from typing import Tuple
+from typing import Any, Tuple
 
 import torch
 from torch.autograd import Function
@@ -16,7 +16,7 @@ class ThreeNN(Function):
     """
 
     @staticmethod
-    def forward(ctx, target: torch.Tensor,
+    def forward(ctx: Any, target: torch.Tensor,
                 source: torch.Tensor) -> Tuple[torch.Tensor, torch.Tensor]:
         """
         Args:
diff --git a/mmcv/ops/upfirdn2d.py b/mmcv/ops/upfirdn2d.py
index 255354dad6..434238359a 100644
--- a/mmcv/ops/upfirdn2d.py
+++ b/mmcv/ops/upfirdn2d.py
@@ -95,6 +95,8 @@
 
 # =======================================================================
 
+from typing import Any, List, Tuple, Union
+
 import torch
 from torch.autograd import Function
 from torch.nn import functional as F
@@ -108,8 +110,10 @@
 class UpFirDn2dBackward(Function):
 
     @staticmethod
-    def forward(ctx, grad_output, kernel, grad_kernel, up, down, pad, g_pad,
-                in_size, out_size):
+    def forward(ctx: Any, grad_output: torch.Tensor, kernel: torch.Tensor,
+                grad_kernel: torch.Tensor, up: tuple, down: tuple, pad: tuple,
+                g_pad: tuple, in_size: Union[List, Tuple],
+                out_size: Union[List, Tuple]) -> torch.Tensor:
 
         up_x, up_y = up
         down_x, down_y = down
@@ -149,7 +153,7 @@ def forward(ctx, grad_output, kernel, grad_kernel, up, down, pad, g_pad,
         return grad_input
 
     @staticmethod
-    def backward(ctx, gradgrad_input):
+    def backward(ctx: Any, gradgrad_input: torch.Tensor) -> tuple:
         kernel, = ctx.saved_tensors
 
         gradgrad_input = gradgrad_input.reshape(-1, ctx.in_size[2],
@@ -177,7 +181,8 @@ def backward(ctx, gradgrad_input):
 class UpFirDn2d(Function):
 
     @staticmethod
-    def forward(ctx, input, kernel, up, down, pad):
+    def forward(ctx: Any, input: torch.Tensor, kernel: torch.Tensor, up: tuple,
+                down: tuple, pad: tuple) -> torch.Tensor:
         up_x, up_y = up
         down_x, down_y = down
         pad_x0, pad_x1, pad_y0, pad_y1 = pad
@@ -222,7 +227,7 @@ def forward(ctx, input, kernel, up, down, pad):
         return out
 
     @staticmethod
-    def backward(ctx, grad_output):
+    def backward(ctx: Any, grad_output: torch.Tensor) -> tuple:
         kernel, grad_kernel = ctx.saved_tensors
 
         grad_input = UpFirDn2dBackward.apply(
@@ -240,7 +245,12 @@ def backward(ctx, grad_output):
         return grad_input, None, None, None, None
 
 
-def upfirdn2d(input, kernel, up=1, down=1, pad=(0, 0)):
+def upfirdn2d(
+    input: torch.Tensor,
+    kernel: torch.Tensor,
+    up: Union[int, tuple] = 1,
+    down: Union[int, tuple] = 1,
+    pad: tuple = (0, 0)) -> torch.Tensor:  # noqa E125
     """UpFRIDn for 2d features.
 
     UpFIRDn is short for upsample, apply FIR filter and downsample. More
@@ -264,14 +274,14 @@ def upfirdn2d(input, kernel, up=1, down=1, pad=(0, 0)):
     """
     if input.device.type == 'cpu':
         if len(pad) == 2:
-            pad = (pad[0], pad[1], pad[0], pad[1])
+            pad = (pad[0], pad[1], pad[0], pad[1])  # type: ignore
 
-        up = to_2tuple(up)
+        _up = to_2tuple(up)
 
-        down = to_2tuple(down)
+        _down = to_2tuple(down)
 
-        out = upfirdn2d_native(input, kernel, up[0], up[1], down[0], down[1],
-                               pad[0], pad[1], pad[2], pad[3])
+        out = upfirdn2d_native(input, kernel, _up[0], _up[1], _down[0],
+                               _down[1], pad[0], pad[1], pad[2], pad[3])
     else:
         _up = to_2tuple(up)
 
@@ -287,8 +297,9 @@ def upfirdn2d(input, kernel, up=1, down=1, pad=(0, 0)):
     return out
 
 
-def upfirdn2d_native(input, kernel, up_x, up_y, down_x, down_y, pad_x0, pad_x1,
-                     pad_y0, pad_y1):
+def upfirdn2d_native(input: torch.Tensor, kernel: torch.Tensor, up_x: int,
+                     up_y: int, down_x: int, down_y: int, pad_x0: int,
+                     pad_x1: int, pad_y0: int, pad_y1: int) -> torch.Tensor:
     _, channel, in_h, in_w = input.shape
     input = input.reshape(-1, in_h, in_w, 1)
 
diff --git a/mmcv/ops/voxelize.py b/mmcv/ops/voxelize.py
index ee4e0ae8f6..992ce68fd2 100644
--- a/mmcv/ops/voxelize.py
+++ b/mmcv/ops/voxelize.py
@@ -1,4 +1,6 @@
 # Copyright (c) OpenMMLab. All rights reserved.
+from typing import Any, List, Tuple, Union
+
 import torch
 from torch import nn
 from torch.autograd import Function
@@ -13,13 +15,14 @@
 class _Voxelization(Function):
 
     @staticmethod
-    def forward(ctx,
-                points,
-                voxel_size,
-                coors_range,
-                max_points=35,
-                max_voxels=20000,
-                deterministic=True):
+    def forward(
+            ctx: Any,
+            points: torch.Tensor,
+            voxel_size: Union[tuple, float],
+            coors_range: Union[tuple, float],
+            max_points: int = 35,
+            max_voxels: int = 20000,
+            deterministic: bool = True) -> Union[Tuple[torch.Tensor], Tuple]:
         """Convert kitti points(N, >=3) to voxels.
 
         Args:
@@ -111,11 +114,11 @@ class Voxelization(nn.Module):
     """
 
     def __init__(self,
-                 voxel_size,
-                 point_cloud_range,
-                 max_num_points,
-                 max_voxels=20000,
-                 deterministic=True):
+                 voxel_size: List,
+                 point_cloud_range: List,
+                 max_num_points: int,
+                 max_voxels: Union[tuple, int] = 20000,
+                 deterministic: bool = True):
         """
         Args:
             voxel_size (list): list [x, y, z] size of three dimension
@@ -149,8 +152,9 @@ def __init__(self,
         point_cloud_range = torch.tensor(
             point_cloud_range, dtype=torch.float32)
         voxel_size = torch.tensor(voxel_size, dtype=torch.float32)
-        grid_size = (point_cloud_range[3:] -
-                     point_cloud_range[:3]) / voxel_size
+        grid_size = (
+            point_cloud_range[3:] -  # type: ignore
+            point_cloud_range[:3]) / voxel_size  # type: ignore
         grid_size = torch.round(grid_size).long()
         input_feat_shape = grid_size[:2]
         self.grid_size = grid_size
@@ -158,7 +162,7 @@ def __init__(self,
         # [w, h, d] -> [d, h, w]
         self.pcd_shape = [*input_feat_shape, 1][::-1]
 
-    def forward(self, input):
+    def forward(self, input: torch.Tensor) -> torch.Tensor:
         if self.training:
             max_voxels = self.max_voxels[0]
         else: