Abstract: Primary users and secondary users coexist in Cognitive Networks at the same time,so the transmission of Secondary Users must not interfere with the transmission of Primary user.The cooperative transmission of Secondary Users can improve the transmission performance of the Secondary Users,so that Cognitive Wireless Network can acquire space and time diversity gain. Before the researcher have proposed a single-relay cooperative transmission strategy. In order to further enhance the system performance of Cognitive Wireless Network.Two-relay collaborative transmission scheme based on amplify and forward is proposed. In this paper, Primary and Secondary Users coexist and Primary Users alternately transfer channel state between busy and leisure.When Primary Users exist,Secondary Users use the relay node to forward data by the chance,and we do the theoretical analysis of conflict-free transmission time and bit error rate of the scheme we propose.The analytical expression of Conflict-free transmission time and bit error rate in the single-relay cooperative transmission and dual-relay cooperative transmission mode are given. Theoretical analysis and simulation results show that,the dual-relay cooperative transmission strategy can further increase conflict-free transmission time and reduce the bit error rate than the single-relay cooperative transmission. Dual-relay cooperative transmission bring considerable performance gain for Cognitive Radio Networks.