diff --git a/parl/env/continuous_wrappers.py b/parl/env/continuous_wrappers.py
index c61181919..ee8808ad5 100644
--- a/parl/env/continuous_wrappers.py
+++ b/parl/env/continuous_wrappers.py
@@ -23,15 +23,17 @@ def __init__(self, env):
         [low_bound, high_bound].
         """
         gym.Wrapper.__init__(self, env)
+
         assert hasattr(
             self.env.action_space,
             'low'), 'action space should be instance of gym.spaces.Box'
         assert hasattr(
             self.env.action_space,
             'high'), 'action space should be instance of gym.spaces.Box'
-        self.low_bound = self.env.action_space.low[0]
-        self.high_bound = self.env.action_space.high[0]
-        assert self.high_bound > self.low_bound
+        self.low_bound = self.env.action_space.low
+        self.high_bound = self.env.action_space.high
+        assert np.all(self.high_bound >= self.low_bound)
+
         if hasattr(env, '_max_episode_steps'):
             self._max_episode_steps = int(self.env._max_episode_steps)
 
diff --git a/parl/env/tests/continuous_wrappers_test.py b/parl/env/tests/continuous_wrappers_test.py
index f7423f200..5c09f939b 100644
--- a/parl/env/tests/continuous_wrappers_test.py
+++ b/parl/env/tests/continuous_wrappers_test.py
@@ -20,7 +20,8 @@
 
 class MockEnv(gym.Env):
     def __init__(self, low, high):
-        self.action_space = gym.spaces.Box(low=low, high=high, shape=(3, ))
+        self.action_space = gym.spaces.Box(
+            low=np.array(low), high=np.array(high))
         self._max_episode_steps = 1000
 
     def step(self, action):
@@ -34,21 +35,33 @@ class TestActionMappingWrapper(unittest.TestCase):
     def test_action_mapping(self):
         origin_act = np.array([-1.0, 0.0, 1.0])
 
-        env = MockEnv(0.0, 1.0)
+        env = MockEnv([0.0] * 3, [1.0] * 3)
         wrapper_env = ActionMappingWrapper(env)
         wrapper_env.step(origin_act)
         self.assertListEqual(list(env.action), [0.0, 0.5, 1.0])
 
-        env = MockEnv(-2.0, 2.0)
+        env = MockEnv([-2.0] * 3, [2.0] * 3)
         wrapper_env = ActionMappingWrapper(env)
         wrapper_env.step(origin_act)
         self.assertListEqual(list(env.action), [-2.0, 0.0, 2.0])
 
-        env = MockEnv(-5.0, 10.0)
+        env = MockEnv([-5.0] * 3, [10.0] * 3)
         wrapper_env = ActionMappingWrapper(env)
         wrapper_env.step(origin_act)
         self.assertListEqual(list(env.action), [-5.0, 2.5, 10.0])
 
+        # test low bound or high bound is different in different dimensions.
+        env = MockEnv([0.0, -2.0, -5.0], [1.0, 2.0, 10.0])
+        wrapper_env = ActionMappingWrapper(env)
+        wrapper_env.step(origin_act)
+        self.assertListEqual(list(env.action), [0.0, 0.0, 10.0])
+
+        origin_act = np.array([0.0, 0.0, 0.0])
+        env = MockEnv([0.0, -2.0, -5.0], [1.0, 2.0, 10.0])
+        wrapper_env = ActionMappingWrapper(env)
+        wrapper_env.step(origin_act)
+        self.assertListEqual(list(env.action), [0.5, 0.0, 2.5])
+
 
 if __name__ == '__main__':
     unittest.main()