diff --git a/swift/llm/utils/client_utils.py b/swift/llm/utils/client_utils.py
index c718c2066..05978cd5c 100644
--- a/swift/llm/utils/client_utils.py
+++ b/swift/llm/utils/client_utils.py
@@ -58,8 +58,8 @@ def _parse_stream_data(data: bytes) -> Optional[str]:
     data = data.strip()
     if len(data) == 0:
         return
-    assert data.startswith('data: '), f'data: {data}'
-    return data[6:].strip()
+    assert data.startswith('data:'), f'data: {data}'
+    return data[5:].strip()
 
 
 def _to_base64(img_path: Union[str, 'PIL.Image.Image', bytes]) -> str: