diff --git a/httprunner/models.py b/httprunner/models.py
index c4b60955..c35886c0 100644
--- a/httprunner/models.py
+++ b/httprunner/models.py
@@ -158,7 +158,7 @@ class StepData(BaseModel):
 
     success: bool = False
     name: Text = ""  # teststep name
-    data: Union[SessionData, List[SessionData]] = None
+    data: Union[SessionData, List['StepData']] = None
     export_vars: VariablesMapping = {}