Abstract: In the P2P environment，parties communicate directly with exchange files or execute transaction in a peer-to-peer fashion.Peers have to manage the risks involved in the collaboration when the information about each other is incomplete.In traditional access control，authorization is assumed to be done before access is allowed.What’s more，the attributes can’t be updated when accessing.So it can’t be applied to the system of attributes dynamically changing very well.The factors that affect the reputation values are taken into account comprehensively.So a more accurate value is got.Then with the UCON model，UCON_P2P model is proposed.Because of the variability of attributes and the continuity of authority of the UCON，this model can be applied to P2P dynamic environment very well.