diff --git a/imperative/python/megengine/data/dataloader.py b/imperative/python/megengine/data/dataloader.py
index 31cce8da4f8c31f399f71a77bb2d9c451a00e06e..c1fb5432043b0557320d01e34757889d09f70d26 100644
--- a/imperative/python/megengine/data/dataloader.py
+++ b/imperative/python/megengine/data/dataloader.py
@@ -19,7 +19,7 @@ import numpy as np
 from ..logger import get_logger
 from ..random.rng import _random_seed_generator
 from .collator import Collator
-from .dataset import Dataset, MapDataset, StreamDataset
+from .dataset import Dataset, StreamDataset
 from .sampler import MapSampler, Sampler, SequentialSampler, StreamSampler
 from .transform import PseudoTransform, Transform
 
@@ -88,7 +88,15 @@ class DataLoader:
 
         self.divide = divide
 
-        if isinstance(dataset, MapDataset):
+        if isinstance(dataset, StreamDataset):
+            self.sampler = sampler if sampler else StreamSampler(batch_size=1)
+            assert isinstance(
+                self.sampler, StreamSampler
+            ), "types of dataset and sampler do not match"
+        else:
+            assert isinstance(
+                dataset, Dataset
+            ), "Can not recognize this kind of dataset: %s" % type(dataset)
             self.sampler = (
                 sampler
                 if sampler
@@ -97,15 +105,6 @@ class DataLoader:
             assert isinstance(
                 self.sampler, MapSampler
             ), "types of dataset and sampler do not match"
-        elif isinstance(dataset, StreamDataset):
-            self.sampler = sampler if sampler else StreamSampler(batch_size=1)
-            assert isinstance(
-                self.sampler, StreamSampler
-            ), "types of dataset and sampler do not match"
-        else:
-            raise TypeError(
-                "can not recognize this kind of dataset: %s" % type(dataset)
-            )
 
         if divide:
             if self.sampler.batch_size <= self.num_workers:
@@ -140,15 +139,14 @@ class DataLoader:
                 return _SerialStreamDataLoaderIter(self)
             else:
                 return _ParallelStreamDataLoaderIter(self)
-        elif isinstance(self.dataset, MapDataset):
+        else:
+            assert isinstance(
+                self.dataset, Dataset
+            ), "Can not recognize this kind of dataset: %s" % type(self.dataset)
             if not self.num_workers:
                 return _SerialMapDataLoaderIter(self)
             else:
                 return _ParallelMapDataLoaderIter(self)
-        else:
-            raise TypeError(
-                "can not recognize this kind of dataset: %s" % type(self.dataset)
-            )
 
     def __len__(self):
         return len(self.sampler)
diff --git a/imperative/python/megengine/data/dataset/__init__.py b/imperative/python/megengine/data/dataset/__init__.py
index 8b70d22111ba33a749a8c90491b2db52a700ed44..2d6fe2f1af4e7d2ecab50a37ad41b4870cf93cf4 100644
--- a/imperative/python/megengine/data/dataset/__init__.py
+++ b/imperative/python/megengine/data/dataset/__init__.py
@@ -6,5 +6,5 @@
 # Unless required by applicable law or agreed to in writing,
 # software distributed under the License is distributed on an
 # "AS IS" BASIS, WITHOUT ARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
-from .meta_dataset import ArrayDataset, Dataset, MapDataset, StreamDataset
+from .meta_dataset import ArrayDataset, Dataset, StreamDataset
 from .vision import *
diff --git a/imperative/python/megengine/data/dataset/meta_dataset.py b/imperative/python/megengine/data/dataset/meta_dataset.py
index 8b2a304d8eb86057d038a794ed40ce51b7e7a7ef..dd1f01c95088712c5132d8e513b4e6d271d97f8b 100644
--- a/imperative/python/megengine/data/dataset/meta_dataset.py
+++ b/imperative/python/megengine/data/dataset/meta_dataset.py
@@ -12,17 +12,7 @@ from typing import Tuple
 
 class Dataset(ABC):
     r"""
-    An abstract class for all Datasets.
-    """
-
-    @abstractmethod
-    def __init__(self):
-        pass
-
-
-class MapDataset(Dataset):
-    r"""
-    An abstract class for map data.
+    An abstract class for all datasets.
     __getitem__ and __len__ method are aditionally needed.
     """
 
@@ -53,8 +43,14 @@ class StreamDataset(Dataset):
     def __iter__(self):
         pass
 
+    def __getitem__(self):
+        raise AssertionError("can not get item from StreamDataset by index")
+
+    def __len__(self):
+        raise AssertionError("StreamDataset does not have length")
+
 
-class ArrayDataset(MapDataset):
+class ArrayDataset(Dataset):
     def __init__(self, *arrays):
         r"""
         ArrayDataset is a dataset for numpy array data, one or more numpy arrays
diff --git a/imperative/python/megengine/data/dataset/vision/meta_vision.py b/imperative/python/megengine/data/dataset/vision/meta_vision.py
index 6d03d3eda5451a05039f513034f32444004db218..f89df740788f0bb1f9a421e21053b33b8fc17d17 100644
--- a/imperative/python/megengine/data/dataset/vision/meta_vision.py
+++ b/imperative/python/megengine/data/dataset/vision/meta_vision.py
@@ -9,10 +9,10 @@
 import collections.abc
 import os
 
-from ..meta_dataset import MapDataset
+from ..meta_dataset import Dataset
 
 
-class VisionDataset(MapDataset):
+class VisionDataset(Dataset):
     _repr_indent = 4
 
     def __init__(self, root, *, order=None, supported_order=None):
diff --git a/imperative/python/test/unit/data/test_dataset.py b/imperative/python/test/unit/data/test_dataset.py
index d68d37846d4b69d784df3d29125fb4c23240e918..4df34921e20cab56b1af7fe9c5dddc1e9623ce66 100644
--- a/imperative/python/test/unit/data/test_dataset.py
+++ b/imperative/python/test/unit/data/test_dataset.py
@@ -12,14 +12,12 @@ import sys
 import numpy as np
 import pytest
 
-from megengine.data.dataset import ArrayDataset, Dataset, MapDataset, StreamDataset
+from megengine.data.dataset import ArrayDataset, Dataset, StreamDataset
 
 
 def test_abstract_cls():
     with pytest.raises(TypeError):
         Dataset()
-    with pytest.raises(TypeError):
-        MapDataset()
     with pytest.raises(TypeError):
         StreamDataset()