diff --git a/tests/test_dataloader_seed.py b/tests/test_dataloader_seed.py
new file mode 100644
index 00000000..7042cdee
--- /dev/null
+++ b/tests/test_dataloader_seed.py
@@ -0,0 +1,60 @@
+import random
+from types import SimpleNamespace
+
+from tools.data import build_dataloader
+
+
+def _config(label_file, seed):
+    return {
+        'Global': {
+            'seed': seed,
+            'distributed': False,
+        },
+        'Train': {
+            'dataset': {
+                'name': 'SimpleDataSet',
+                'data_dir': str(label_file.parent),
+                'label_file_list': [str(label_file)],
+                'ratio_list': [0.5],
+                'transforms': [],
+            },
+            'loader': {
+                'batch_size_per_card': 1,
+                'drop_last': False,
+                'num_workers': 0,
+                'pin_memory': False,
+                'shuffle': True,
+            },
+        },
+    }
+
+
+def _data_order(label_file, process_seed, explicit_seed=None):
+    logger = SimpleNamespace(info=lambda *args: None, error=lambda *args: None)
+    random.seed(process_seed)
+    loader = build_dataloader(
+        _config(label_file, process_seed),
+        'Train',
+        logger,
+        seed=explicit_seed,
+        task='det',
+    )
+    return loader.dataset.data_lines
+
+
+def test_simple_dataset_preserves_process_and_explicit_seeds(tmp_path):
+    label_file = tmp_path / 'labels.txt'
+    label_file.write_text(
+        ''.join(f'image-{i}.jpg\t[]\n' for i in range(40)),
+        encoding='utf-8',
+    )
+
+    seed_48_first = _data_order(label_file, 48)
+    seed_48_second = _data_order(label_file, 48)
+    seed_49 = _data_order(label_file, 49)
+    explicit_7_after_48 = _data_order(label_file, 48, explicit_seed=7)
+    explicit_7_after_49 = _data_order(label_file, 49, explicit_seed=7)
+
+    assert seed_48_first == seed_48_second
+    assert seed_48_first != seed_49
+    assert explicit_7_after_48 == explicit_7_after_49
diff --git a/tools/data/simple_dataset.py b/tools/data/simple_dataset.py
index 61477c9e..249ddea9 100644
--- a/tools/data/simple_dataset.py
+++ b/tools/data/simple_dataset.py
@@ -80,14 +80,16 @@ def get_image_info_list(self, file_list, ratio_list):
             with open(file, 'rb') as f:
                 lines = f.readlines()
                 if self.mode == 'train' or ratio_list[idx] < 1.0:
-                    random.seed(self.seed)
+                    if self.seed is not None:
+                        random.seed(self.seed)
                     lines = random.sample(lines,
                                           round(len(lines) * ratio_list[idx]))
                 data_lines.extend(lines)
         return data_lines
 
     def shuffle_data_random(self):
-        random.seed(self.seed)
+        if self.seed is not None:
+            random.seed(self.seed)
         random.shuffle(self.data_lines)
         return