Abstract: Similar to the interpersonal relationship network, the issue of mutual trust exists in P2P file-sharing transactions. Through analyzing the trust relationship between requesting peers and providing peers in volving in P2P file-sharing transactions, a bidirectional parallel trust mechanism, called BPTM, is proposed. This mechanism deals with the problem of mutual trust between requesting peers and providing peers, on the basis of which the trust model of service selection and the trust model of service response are constructed to perform the bidirectional evaluation of trust relationship. The simulation and analysis show that BPTM is more advanced in successful transaction rate than traditional unidirectional trust mechanism. So the trust mechanism can perform much better in establishing mutual relationships among peers.