Trust problem is a key issue for Mobile P2P (MP2P) network security. In MP2P network, terminals addressing mode, communication way and display identifier are different to traditional P2P network. Some security issues such as: malicious slander and collusion, free ride phenomenon, are even more serious compared to traditional P2P network. Aimed at these above issues, a Proxy-based Security-Feedback Trust Model (PSTM) is proposed. Different types of terminals access to different proxy servers to shield the discrepancy between different terminal equipments on MP2P equipment access network layer. Meanwhile, proxy servers can reduce the problem of single point failure with method of trust related tables backup and recovery. Certificate Feedback Raters identification and qualification through security resource-selection protocol then integrate trust information according to similarity of terminal and resource types with weight. Furthermore, set global contribution value and evaluation value in multi-granularity trust computation to motivate mobile peers honest feedbacks. Divide mobile peers direct trust value into peer-oriented and resource-oriented values to make trust feedbacks more authentic. Simulation experiments show that PSTM can reduce malicious slander and collusion effectively. It also can restrain self-ish peers free ride behaviors and increase successful cooperation rate of high-contributed nodes in MP2P network.