In order to improve the security of database system and resist threat from all aspects, especially the threat from database administrators, the paper designed a new database encryption system. In this system sensitive information is encrypted and establishes ciphertext address index table for it. Encryptions for character fields and numeric fields have different processing methods. Decryption key should be synthesized by both client and server. System can execute SQL query like equality queries, range queries and so on which are difficult to deal with after encryption. The analysis shows that the system has better security.