In order to accomplish the task, peer-to-peer (P2P) systems rely on the cooperation of the peers. Ease is a threat to the security of the P2P system may perform malicious activities. When you create a trust long-term relationships between peers, by reducing the risks and uncertainties in the interaction of P2P in the future, you will be able to provide a more secure environment. However, establishing a trust entity unknown, it is difficult for malicious environment. In addition, be measured in a numerical concept and social, it is difficult to trust. Metric is required to represent the reliability of the calculation model. Is not enough in most cases to classify the peers as either reliable, or of unreliable. It is possible that peer to rank according to reliability, you must have the accuracy of the metric. Peer feedback and interaction, provides information for determining the trust between the peers. Interaction with peers, provides certain information about the peer, but there are cases where false information is included feedback. Evaluation of reliability will be an issue this.