Query expansion has long been suggested as a technique for dealing with the fundamental issue of word mismatch in information retrieval and it has gained great success in Web searching. However, processing query expansion is very challenging in hybrid P2P network because a P2P system is a decentralized and dynamic system. First, the LEM query expansion method, which is constructed by analyzing correlation between queries and documents, is presented. And then, the HEM query expansion method is proposed by establishing the correlation between queries and documents terms directly. Next, an efficient search algorithm is constructed based on the query expansion algorithms. It is proved by experiments that the query expansion methods and search algorithms can greatly improve the search efficiency.