In the thesis, a solution of query against encrypted XML data is developed. The solution relies on the QueryAware Decryption method in Reference［1］,which allows us to decrypt only those parts that contribute to the query result. Our solution applies Hash tables and chained lists to create the index of user keys, and disseminates an encrypted XML index along with the encrypted XML data. As the decrypted index outputs where the query results are located in the encrypted XML data, the unnecessary decryption can be prevented for the other parts of the data. The experimental results show that the method improves the performance of query processing, efficiently avoids decrypting nonrelative data, subtly reduces the amount of user keys exchange,and solves the dissemination of user keys.