Abstract: The existence of selfish and malicious peers and their non-collaborative behaviors heavily damage the whole performance of the peer-to-peer system.Making an analysis to a rank-based incentive mechanism which was proposed by Habib, found that there were some deficiencies in this incentive mechanism.Thus, an improved rank-based incentive mechanism was proposed which could urge selfish peers to behave collaboratively.The preliminary results verify that the improved incentive mechanism provides a good quality of service and availably control the behaviors of selfish peers.