Currently, Peer-to-Peer Network(P2P network), as a newly developed Internet application architecture, are developing rapidly and attracting increasing attention from industries and academic researchers since the great growth of Internet. Meantime, its application expands and goes deeply. However, as the researches and study of this field going further, the deficiencies of P2P, such as the autonomy feature of the peers has negative impact on system operation, are revealed. The autonomy feature of the peers results in its self-interest maximization at the cost of ignoring the autonomy feature of the peers in network protocols which gives rise to free rider and finally damages the fairness among peers. What’s worse, it would affect the system operation. The cooperation mechanism among peers was studied to resolve the problem introduced by the autonomy feature of peers. The study about enforce cooperation among pees in order to achieve the object of the system and promote the cooperation among peers in order to improve the efficiency of the system on premise that protect the fairness of the peers. In this work, we present the mechanism of cooperation of peers in P2P network and the influence on the performance of P2P network.The study in this work includes:(1)The survey and analysis of present findings of the research of the cooperation mechanism of the peers in P2P networks, find out the usual method and analysis the essence of the cooperation mechanism as the foundation of our study.(2)Our research focuses on the cooperation mechanism of peers in P2P network based vertical search engine system. We proposal a new data distribution policy base called LRS on the cooperation of peers and LRS based index syncopation. LRS has characteristics of high data available, less bandwidth consuming, load balance among peers and LRS based index syncopation can improve the efficiency of index search.(3)We also propose a versatile cooperation mechanism, Hermes, which peer could ask for cooperative service according to their own requirement. It is based on the management of credit and avoids free rider successfully. Hermes mechanism enhances the efficiency among cooperative peers by meeting the autonomy feature of the peers for better cooperation.(4)Our research study the BitTorrent system and we simulate the BitTorrent system and implement Hermes mechanism in the simulated BitTorrent system. We study the influence of cooperation mechanism by experiment result.