Abstract: A joint random sensing policy is proposed by using the inactive secondary users in the cognitive network, which is different from previous cognitive radio sensing researches. The policy is proposed due to the uncertainty of primary users states and the problem of inability for the random sensing policy to find out vacant channels rapidly. After utilizing inactive secondary users to detect, sensing performance of cognitive networks can be deduced by modeling the list of available channels stored in cognitive base station as Markov model. Both the theoretical analysis and simulating results show that sensing with inactive cognitive users can reduce the service overhead and improve the cognitive network throughput. After considering the report overhead of secondary users, the optimal number of inactive users is obtained which yields the highest throughput of cognitive network through an optimization algorithm.