diff --git a/httprunner/schema/api.py b/httprunner/schema/api.py
index eb7c0b5e..6744dd79 100644
--- a/httprunner/schema/api.py
+++ b/httprunner/schema/api.py
@@ -8,7 +8,7 @@ from httprunner.schema import common
 class Api(BaseModel):
     name: common.Name
     request: common.Request
-    variables: common.Variables
+    variables: common.Variables = {}
     base_url: common.BaseUrl = ""
     setup_hooks: common.Hook = []
     teardown_hooks: common.Hook = []