Trust plays an important role in making collaborative decisions, so the trust problem in P2P networks has become a focus of research. In this paper, a fuzz set based model is proposed for building trust and reputation in P2P collaborations based on observations and recommendations, and using fuzzy set a peer can present differentiated trust and combine different aspects of trust in collaborations. Depending on fuzzy similarity measure, a good recommenders set can be maintained. The evaluation of the model using simulation experiments shows its effectiveness.