diff --git a/tianshou/env/vecenv/asyncenv.py b/tianshou/env/vecenv/asyncenv.py
index 00d1e51ca..75ffc4465 100644
--- a/tianshou/env/vecenv/asyncenv.py
+++ b/tianshou/env/vecenv/asyncenv.py
@@ -52,10 +52,12 @@ def _assert_and_transform_id(self,
         return id
 
     def reset(self, id: Optional[Union[int, List[int]]] = None) -> np.ndarray:
+        self._assert_is_closed()
         id = self._assert_and_transform_id(id)
         return super().reset(id)
 
     def render(self, **kwargs) -> List[Any]:
+        self._assert_is_closed()
         if len(self.waiting_id) > 0:
             raise RuntimeError(
                 f"Environments {self.waiting_id} are still "
@@ -80,6 +82,7 @@ def step(self,
         (initially they are env_ids of all the environments). If action is
         ``None``, fetch unfinished step() calls instead.
         """
+        self._assert_is_closed()
         if action is not None:
             id = self._assert_and_transform_id(id)
             assert len(action) == len(id)
diff --git a/tianshou/env/vecenv/base.py b/tianshou/env/vecenv/base.py
index b6c160dab..f4897b5c4 100644
--- a/tianshou/env/vecenv/base.py
+++ b/tianshou/env/vecenv/base.py
@@ -48,6 +48,10 @@ def __len__(self) -> int:
         """Return len(self), which is the number of environments."""
         return self.env_num
 
+    def __del__(self):
+        """Close the environment before garbage collected"""
+        self.close()
+
     def __getattribute__(self, key: str):
         """Switch between the default attribute getter or one
            looking at wrapped environment level depending on the key."""
diff --git a/tianshou/env/vecenv/shmemenv.py b/tianshou/env/vecenv/shmemenv.py
index a764ba6d3..9eda9045e 100644
--- a/tianshou/env/vecenv/shmemenv.py
+++ b/tianshou/env/vecenv/shmemenv.py
@@ -124,6 +124,7 @@ def step(self,
              action: np.ndarray,
              id: Optional[Union[int, List[int]]] = None
              ) -> Tuple[np.ndarray, np.ndarray, np.ndarray, np.ndarray]:
+        self._assert_is_closed()
         if id is None:
             id = range(self.env_num)
         elif np.isscalar(id):
@@ -140,6 +141,7 @@ def step(self,
         return obs, rew, done, info
 
     def reset(self, id: Optional[Union[int, List[int]]] = None) -> np.ndarray:
+        self._assert_is_closed()
         if id is None:
             id = range(self.env_num)
         elif np.isscalar(id):
diff --git a/tianshou/env/vecenv/subproc.py b/tianshou/env/vecenv/subproc.py
index 9b8d8e2f3..de476afea 100644
--- a/tianshou/env/vecenv/subproc.py
+++ b/tianshou/env/vecenv/subproc.py
@@ -60,6 +60,7 @@ def __init__(self, env_fns: List[Callable[[], gym.Env]]) -> None:
             c.close()
 
     def __getattr__(self, key):
+        self._assert_is_closed()
         for p in self.parent_remote:
             p.send(['getattr', key])
         return [p.recv() for p in self.parent_remote]
@@ -68,6 +69,7 @@ def step(self,
              action: np.ndarray,
              id: Optional[Union[int, List[int]]] = None
              ) -> Tuple[np.ndarray, np.ndarray, np.ndarray, np.ndarray]:
+        self._assert_is_closed()
         if id is None:
             id = range(self.env_num)
         elif np.isscalar(id):
@@ -80,6 +82,7 @@ def step(self,
         return obs, rew, done, info
 
     def reset(self, id: Optional[Union[int, List[int]]] = None) -> np.ndarray:
+        self._assert_is_closed()
         if id is None:
             id = range(self.env_num)
         elif np.isscalar(id):
@@ -90,6 +93,7 @@ def reset(self, id: Optional[Union[int, List[int]]] = None) -> np.ndarray:
         return obs
 
     def seed(self, seed: Optional[Union[int, List[int]]] = None) -> List[int]:
+        self._assert_is_closed()
         if np.isscalar(seed):
             seed = [seed + _ for _ in range(self.env_num)]
         elif seed is None:
@@ -99,11 +103,13 @@ def seed(self, seed: Optional[Union[int, List[int]]] = None) -> List[int]:
         return [p.recv() for p in self.parent_remote]
 
     def render(self, **kwargs) -> List[Any]:
+        self._assert_is_closed()
         for p in self.parent_remote:
             p.send(['render', kwargs])
         return [p.recv() for p in self.parent_remote]
 
     def close(self) -> List[Any]:
+        "Instances of SubprocVectorEnv should not called again once"
         if self.closed:
             return []
         for p in self.parent_remote:
@@ -113,3 +119,7 @@ def close(self) -> List[Any]:
         for p in self.processes:
             p.join()
         return result
+
+    def _assert_is_closed(self):
+        assert not self.closed, \
+             f"Methods of {self.__class__.__name__} should not be called after closed."