Abstract: This paper proposes a time-decay based trust model in peer-to-peer networks.Through the transaction time is faded，the proposed model makes trust value changed dynamically with time decay，which achieves the goal that the more transaction closes to，the more reliable it is.Finally this paper presents the experimental protocol and simulation.The experimental result shows that the proposed model is more approached fact value and it can resist vicious association attraction，dynamic strategy attraction，and it has a favorable performance.

Key words: peer-to-peer networks, partial trust, recommended confidence, time factor

摘要： 提出了一种基于时间衰减的P2P信任模型。通过交易时间的衰减，利用加权的方式使得信任值随着时间的衰减产生动态变化，达到了距离现在越近，交易的信息越可靠的目的，最后给出了实验的协议及仿真实验。实验结果表明，该模型计算更逼近真实值，且能抵抗恶意联合攻击、动态策略型攻击等安全威胁，具有良好的性能。

关键词: 对等网络, 局部信任, 推荐信任, 时间因子