The present disclosure discloses a credit messaging system, a credit data storage method, a device, and a medium, and belongs to the field of network technologies. A server generates a unified user identifier based on user information of a user, generates, based on behavioral data of the user, credit data of the user through calculation by using a unified algorithm, and then, stores the credit data of the user and a corresponding user identifier into a block chain by using a target policy. In a block chain system, a unified user identifier is obtained for a same user, so that organizations in the block chain system may query credit data of the user according to the unified user identifier, thereby implementing high-quality data circulation and transactions while improving accuracy and comprehensiveness of queries for the credit data. In addition, credit data is generated according to a unified algorithm, thereby ensuring regulation of the credit data, and improving a reference value of the credit data of the organizations.