Abstract: In the aspect of query decomposition, a decomposition algorithm based on global metadata dictionary was designed, and the accuracy of the algorithm was proved by an example.In the query optimization, an query optimization algorithm based on XML Schema was proposed.This method could effectively deal with the//and*cases in the path expression, and maked full use of the local data source XML Schema information to reduce the query node range, decreased the times of connection operation and improved the query efficiency of integration system.