diff --git a/modelscope/preprocessors/multi_modal.py b/modelscope/preprocessors/multi_modal.py
index a3411a73..2a5cd259 100644
--- a/modelscope/preprocessors/multi_modal.py
+++ b/modelscope/preprocessors/multi_modal.py
@@ -76,7 +76,10 @@ class OfaPreprocessor(Preprocessor):
         else:
             data = self._build_dict(input)
         sample = self.preprocess(data)
-        sample['sample'] = data
+        str_data = dict()
+        for k, v in data.items():
+            str_data[k] = str(v)
+        sample['sample'] = str_data
         return collate_fn([sample],
                           pad_idx=self.tokenizer.pad_token_id,
                           eos_idx=self.tokenizer.eos_token_id)
diff --git a/tests/pipelines/test_ofa_tasks.py b/tests/pipelines/test_ofa_tasks.py
index 63efa334..1dc7d303 100644
--- a/tests/pipelines/test_ofa_tasks.py
+++ b/tests/pipelines/test_ofa_tasks.py
@@ -1,6 +1,8 @@
 # Copyright (c) Alibaba, Inc. and its affiliates.
 import unittest
 
+from PIL import Image
+
 from modelscope.models import Model
 from modelscope.outputs import OutputKeys
 from modelscope.pipelines import pipeline
@@ -181,8 +183,8 @@ class OfaTasksTest(unittest.TestCase):
             task=Tasks.image_captioning,
             model=model,
         )
-        result = img_captioning(
-            {'image': 'data/test/images/image_captioning.png'})
+        image = Image.open('data/test/images/image_captioning.png')
+        result = img_captioning(image)
         print(result[OutputKeys.CAPTION])
 
     @unittest.skipUnless(test_level() >= 1, 'skip test in current test level')