P2P systems are usually used for information exchange between peers in recent years. However, the open and anonymous nature of a P2P network makes it an ideal medium for malicious peers. There is a lack of efficient mechanism for existing P2P systems to avoid from free riding, whitewashing, collusion and malicious attackers. In this paper, we describe a novel role-base trust model for P2P file sharing system. First, we give object criteria to track each peer's contribution to the system. Second, according to their contribution we divide all the peers into 2 parts: super peers and normal peers. Each of the 2 roles is bonded with different rights and obligations. Third, we show how to carry out the computation and storage at local and global. Finally, we discuss how our trust model allows peer to revoke relationships with distrusted peers. We present a concrete method to validate the proposed trust model and report sets of simulation-based experiments, showing the feasibility and robustness of this model.