In a multidatabase system with an object-oriented data model as a common data model, query processing on schema integration semantics should not only implement the translation from a query against integrated schema to queries against export schema, but also reduce the datum used for answering for user's query as more as possible and ensure the correctness of object reference in semantics. To achieve this object, in this paper, the authors present some new concepts, query processing rules and query processing methods for path expression on schema integration semantics.