diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index abde1fa8..058025a2 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -4,7 +4,8 @@
 
 **Fixed**
 
-- fix: jsonschema, variables maybe in string type, e.g. '${get_variables()}'
+- fix json schema: variables maybe in string type, e.g. '${prepare_variables()}'
+- fix json schema: post json maybe in string type, e.g. '${prepare_post_data()}', '$post_data'
 
 ## 2.5.2 (2020-01-02)
 
diff --git a/httprunner/loader/schemas/common.schema.json b/httprunner/loader/schemas/common.schema.json
index 57b36b28..ce5a33e4 100644
--- a/httprunner/loader/schemas/common.schema.json
+++ b/httprunner/loader/schemas/common.schema.json
@@ -26,8 +26,10 @@
                 },
                 {
                     "type": "string",
+                    "pattern": "^\\$.*",
                     "examples": [
-                        "${get_variables()}"
+                        "${prepare_variables()}",
+                        "${prepare_variables($a, $b)}"
                     ]
                 }
             ]
@@ -116,8 +118,21 @@
                     ]
                 },
                 "json": {
-                    "description": "request body in json format",
-                    "type": "object"
+                    "oneOf": [
+                        {
+                            "description": "request body in json format",
+                            "type": "object"
+                        },
+                        {
+                            "description": "request body in string format, e.g. '${prepare_json($a, $b)}'",
+                            "type": "string",
+                            "pattern": "^\\$.*",
+                            "examples": [
+                                "$post_data",
+                                "${prepare_post_data($a, $b)}"
+                            ]
+                        }
+                    ]
                 },
                 "headers": {
                     "description": "request headers",