diff --git a/CMakeLists.txt b/CMakeLists.txt
index edb9a46c03ab8..a4357f5d155d0 100755
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -209,7 +209,7 @@ option(WITH_STRIP       "Strip so files of Whl packages"         OFF)
 
 # PY_VERSION
 if(NOT PY_VERSION)
-  set(PY_VERSION 2.7)
+  set(PY_VERSION 3.6)
 endif()
 set(PYBIND11_PYTHON_VERSION ${PY_VERSION})
 
diff --git a/python/requirements.txt b/python/requirements.txt
index 14bd5e7caa6f5..e9da2aa24d6cb 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -1,5 +1,4 @@
 requests>=2.20.0
-numpy>=1.13, <=1.16.4 ; python_version<"3.5"
 numpy>=1.13 ; python_version>="3.5" and platform_system != "Windows"
 numpy>=1.13, <=1.19.3 ; python_version>="3.5" and platform_system == "Windows"
 protobuf>=3.1.0
@@ -7,5 +6,5 @@ gast>=0.3.3, <=0.4.0 ; platform_system != "Windows"
 gast==0.3.3 ; platform_system == "Windows"
 Pillow
 six
-decorator==4.4.2
+decorator
 astor
diff --git a/python/unittest_py/requirements.txt b/python/unittest_py/requirements.txt
index 752f3545c69cc..8fd1be69a3d7f 100644
--- a/python/unittest_py/requirements.txt
+++ b/python/unittest_py/requirements.txt
@@ -4,10 +4,8 @@ pycrypto ; platform_system != "Windows"
 mock
 gym
 opencv-python<=4.2.0.32
-visualdl ; python_version>="3.5"
+visualdl
 paddle2onnx>=0.4
-scipy>=0.19.0, <=1.2.1 ; python_version<"3.5"
-scipy<=1.3.1 ; python_version=="3.5"
-scipy ; python_version>"3.5"
+scipy
 prettytable
 distro
diff --git a/tools/count_api_without_core_ops.py b/tools/count_api_without_core_ops.py
index 664b94a059f5c..7af597600e001 100644
--- a/tools/count_api_without_core_ops.py
+++ b/tools/count_api_without_core_ops.py
@@ -37,10 +37,7 @@
 def md5(doc):
     try:
         hashinst = hashlib.md5()
-        if platform.python_version()[0] == "2":
-            hashinst.update(str(doc))
-        else:
-            hashinst.update(str(doc).encode('utf-8'))
+        hashinst.update(str(doc).encode('utf-8'))
         md5sum = hashinst.hexdigest()
     except UnicodeDecodeError as e:
         md5sum = None
diff --git a/tools/print_signatures.py b/tools/print_signatures.py
index 6de9d84379fea..be32ef09b70d6 100644
--- a/tools/print_signatures.py
+++ b/tools/print_signatures.py
@@ -36,10 +36,7 @@
 def md5(doc):
     try:
         hashinst = hashlib.md5()
-        if platform.python_version()[0] == "2":
-            hashinst.update(str(doc))
-        else:
-            hashinst.update(str(doc).encode('utf-8'))
+        hashinst.update(str(doc).encode('utf-8'))
         md5sum = hashinst.hexdigest()
     except UnicodeDecodeError as e:
         md5sum = None
@@ -142,7 +139,7 @@ def visit_member(parent_name, member, member_name=None):
 
 
 def is_primitive(instance):
-    int_types = (int, long) if platform.python_version()[0] == "2" else (int, )
+    int_types = (int, )
     pritimitive_types = int_types + (float, str)
     if isinstance(instance, pritimitive_types):
         return True
diff --git a/tools/sampcd_processor.py b/tools/sampcd_processor.py
index a1658e3c2edf7..f243ada073634 100644
--- a/tools/sampcd_processor.py
+++ b/tools/sampcd_processor.py
@@ -389,7 +389,7 @@ def execute_samplecode(tfname):
     """
     result = True
     msg = None
-    if platform.python_version()[0] in ["2", "3"]:
+    if platform.python_version()[0] in ["3"]:
         cmd = [sys.executable, tfname]
     else:
         logger.error("Error: fail to parse python version!")