diff --git a/mmseg/datasets/chase_db1.py b/mmseg/datasets/chase_db1.py
index 7f14b2da0..5cdc8d8d4 100644
--- a/mmseg/datasets/chase_db1.py
+++ b/mmseg/datasets/chase_db1.py
@@ -1,5 +1,4 @@
 # Copyright (c) OpenMMLab. All rights reserved.
-import os.path as osp
 
 from .builder import DATASETS
 from .custom import CustomDataset
@@ -25,4 +24,4 @@ class ChaseDB1Dataset(CustomDataset):
             seg_map_suffix='_1stHO.png',
             reduce_zero_label=False,
             **kwargs)
-        assert osp.exists(self.img_dir)
+        assert self.file_client.exists(self.img_dir)
diff --git a/mmseg/datasets/custom.py b/mmseg/datasets/custom.py
index fe29dcf9c..2649a5814 100644
--- a/mmseg/datasets/custom.py
+++ b/mmseg/datasets/custom.py
@@ -68,6 +68,9 @@ class CustomDataset(Dataset):
             Default: None
         gt_seg_map_loader_cfg (dict, optional): build LoadAnnotations to
             load gt for evaluation, load from disk by default. Default: None.
+        file_client_args (dict): Arguments to instantiate a FileClient.
+            See :class:`mmcv.fileio.FileClient` for details.
+            Defaults to ``dict(backend='disk')``.
     """
 
     CLASSES = None
@@ -87,7 +90,8 @@ class CustomDataset(Dataset):
                  reduce_zero_label=False,
                  classes=None,
                  palette=None,
-                 gt_seg_map_loader_cfg=None):
+                 gt_seg_map_loader_cfg=None,
+                 file_client_args=dict(backend='disk')):
         self.pipeline = Compose(pipeline)
         self.img_dir = img_dir
         self.img_suffix = img_suffix
@@ -105,6 +109,9 @@ class CustomDataset(Dataset):
         ) if gt_seg_map_loader_cfg is None else LoadAnnotations(
             **gt_seg_map_loader_cfg)
 
+        self.file_client_args = file_client_args
+        self.file_client = mmcv.FileClient.infer_client(self.file_client_args)
+
         if test_mode:
             assert self.CLASSES is not None, \
                 '`cls.CLASSES` or `classes` should be specified when testing'
@@ -146,16 +153,21 @@ class CustomDataset(Dataset):
 
         img_infos = []
         if split is not None:
-            with open(split) as f:
-                for line in f:
-                    img_name = line.strip()
-                    img_info = dict(filename=img_name + img_suffix)
-                    if ann_dir is not None:
-                        seg_map = img_name + seg_map_suffix
-                        img_info['ann'] = dict(seg_map=seg_map)
-                    img_infos.append(img_info)
+            lines = mmcv.list_from_file(
+                split, file_client_args=self.file_client_args)
+            for line in lines:
+                img_name = line.strip()
+                img_info = dict(filename=img_name + img_suffix)
+                if ann_dir is not None:
+                    seg_map = img_name + seg_map_suffix
+                    img_info['ann'] = dict(seg_map=seg_map)
+                img_infos.append(img_info)
         else:
-            for img in mmcv.scandir(img_dir, img_suffix, recursive=True):
+            for img in self.file_client.list_dir_or_file(
+                    dir_path=img_dir,
+                    list_dir=False,
+                    suffix=img_suffix,
+                    recursive=True):
                 img_info = dict(filename=img)
                 if ann_dir is not None:
                     seg_map = img.replace(img_suffix, seg_map_suffix)
diff --git a/mmseg/datasets/drive.py b/mmseg/datasets/drive.py
index 650991147..d44fb0da7 100644
--- a/mmseg/datasets/drive.py
+++ b/mmseg/datasets/drive.py
@@ -1,5 +1,4 @@
 # Copyright (c) OpenMMLab. All rights reserved.
-import os.path as osp
 
 from .builder import DATASETS
 from .custom import CustomDataset
@@ -25,4 +24,4 @@ class DRIVEDataset(CustomDataset):
             seg_map_suffix='_manual1.png',
             reduce_zero_label=False,
             **kwargs)
-        assert osp.exists(self.img_dir)
+        assert self.file_client.exists(self.img_dir)
diff --git a/mmseg/datasets/hrf.py b/mmseg/datasets/hrf.py
index e4e10aeaf..cf3ea8d79 100644
--- a/mmseg/datasets/hrf.py
+++ b/mmseg/datasets/hrf.py
@@ -1,5 +1,4 @@
 # Copyright (c) OpenMMLab. All rights reserved.
-import os.path as osp
 
 from .builder import DATASETS
 from .custom import CustomDataset
@@ -25,4 +24,4 @@ class HRFDataset(CustomDataset):
             seg_map_suffix='.png',
             reduce_zero_label=False,
             **kwargs)
-        assert osp.exists(self.img_dir)
+        assert self.file_client.exists(self.img_dir)
diff --git a/mmseg/datasets/isaid.py b/mmseg/datasets/isaid.py
index d6108b280..db24f9376 100644
--- a/mmseg/datasets/isaid.py
+++ b/mmseg/datasets/isaid.py
@@ -1,5 +1,4 @@
 # Copyright (c) OpenMMLab. All rights reserved.
-import os.path as osp
 
 import mmcv
 from mmcv.utils import print_log
@@ -35,7 +34,7 @@ class iSAIDDataset(CustomDataset):
             seg_map_suffix='.png',
             ignore_index=255,
             **kwargs)
-        assert osp.exists(self.img_dir)
+        assert self.file_client.exists(self.img_dir)
 
     def load_annotations(self,
                          img_dir,
diff --git a/mmseg/datasets/pascal_context.py b/mmseg/datasets/pascal_context.py
index 1e7a09d72..efacee0f3 100644
--- a/mmseg/datasets/pascal_context.py
+++ b/mmseg/datasets/pascal_context.py
@@ -1,5 +1,4 @@
 # Copyright (c) OpenMMLab. All rights reserved.
-import os.path as osp
 
 from .builder import DATASETS
 from .custom import CustomDataset
@@ -52,7 +51,7 @@ class PascalContextDataset(CustomDataset):
             split=split,
             reduce_zero_label=False,
             **kwargs)
-        assert osp.exists(self.img_dir) and self.split is not None
+        assert self.file_client.exists(self.img_dir) and self.split is not None
 
 
 @DATASETS.register_module()
@@ -101,4 +100,4 @@ class PascalContextDataset59(CustomDataset):
             split=split,
             reduce_zero_label=True,
             **kwargs)
-        assert osp.exists(self.img_dir) and self.split is not None
+        assert self.file_client.exists(self.img_dir) and self.split is not None