Trust management is one of the key problems in the P2P systems and e-commerce. Before they have the transaction, people always want to know whether the other side of the transaction partners can be trusted and how much degree of their trustworthiness. This paper proposes a trustable approach based on fuzzy inference in P2P systems and gives a detail discussion of fuzzy inference. They can inference their trust against the trustworthiness of the rules and compute the trustworthiness of the conclusion. This approach is adapted to the P2P environment which the rule and the proof which may be showed as fuzzy, and the approach also have practical meaning for us to build an effective P2P system.