To improve the performance of querying over encrypted character string in database, this paper proposes a method that creating B^* tree cluster index base on index characteristic code. Every encrypted data has an index characteristic code which store in an index filed as index. When querying the encrypted character data, applies the principle of two_phase query. In the first place, make use of index characteristic code to filter the records which is not related to the querying condition. Secondly, decrypt the rest records and take advantage of plaintext querying condition to get the final records. Results of experiments validate the performance of our method compared with exsiting ways at present.