diff --git a/httprunner/step_request.py b/httprunner/step_request.py
index 81f1015b..1f827ea2 100644
--- a/httprunner/step_request.py
+++ b/httprunner/step_request.py
@@ -72,13 +72,13 @@ def run_step_request(runner: HttpRunner, step: TStep) -> StepResult:
         name=step.name,
         success=False,
     )
-    step_variables = runner.merge_step_variables(step.variables)
     start_time = time.time()
 
-
     # parse
     functions = runner.parser.functions_mapping
     prepare_upload_step(step, functions)
+    # step_variables should be defined after prepare_upload_step
+    step_variables = runner.merge_step_variables(step.variables)
     request_dict = step.request.dict()
     request_dict.pop("upload", None)
     parsed_request_dict = runner.parser.parse_data(request_dict, step_variables)