Abstract: To solve the problem of the transaction security in P2P network, by simulating interpersonal interactive process in society network, a subjective trust model is proposed base on cloud model theory. The created definition of the trust cloud and the standard cloud in the evaluation model shows the ambiguity and randomicity of the trust and realizes transferring quantitative data to qualitative data. Based on algorithm of converse trust cloud and trust merging and similarity, comprehensive evaluation and decision-making of subjective trust is realized. The results of experiments show that the trust evaluation model is valid. The model proposed in this paper provides a new way for studying trust management in open networks.