Abstract: The data integrity is an important content of the database protection. In view of database application from one-tier architecture to multi-tier architecture, this paper analyzes the tiered models of the access to database by database application. The realization of the data integrity at each tier is discussed and the examples for the realization in three tiers of database, data module and user interface are given to prove the discussion. Therefore the data integrity can be kept at tiers whenever the access of the data is realized in different process.