Incentive mechanism in P2P is a important problem. The models of new and successful computing requires the development of appropriate incentive mechanisms that are consistent with the enabling technologies. Our paper presents a contingent auction incentive mechanism in P2P environment. All resources are marked price in virtual money, The peers bid for resources in an auction to determine who can get the resources by pay for it with virtual money. The peers can get virtual money through share their resources So the peers? maximize their revenue, if every peer maximize their revenue or resources utility. We achieve the goal that rational and self-interest peers would like to share their resources.