One way to minimize threats in P2P system is to exploit reputation to help evaluate the trustworthiness and predict the future behaviors of peers. Most existing methods for trust management, which are based on reputation, focus on preventing network from the malicious peers. In fact, peers' capabilities to fulfill the tasks are also important factors, which will greatly impact the efficiency of P2P applications. In this study, a set of parameters were identified for describing the trust of a peer. And a trust model based on fuzzy techniques is presented. In simulation, this trust model has been shown to improve the efficiency of P2P system by significantly decreasing the number of inauthentic files on the network.