Abstract: In order to improve the response performance and decrease the transmission interruption probability, a centralized spectrum allocation strategy with an access threshold and super-slot for cognitive radio networks is proposed by limiting the number of data packets in the system and allowing the primary users access spectrum with a pre-emptive priority based on a super-slot. Through combining the sequence number of the specified slot in a super-slot and the number of data packets for the cognitive users in the system, a two-dimensional discrete-time Markov chain model is established presenting the formulas for the performance measures in terms of the average latency, the throughput and the channel switching ratio as well. A profit function is created; the access threshold is optimized for different super-slot sizes and the system experiments are conducted via the use of the optimization results. The experiment results show that a reasonable access threshold and a proper super-slot size can improve the transmission quality for the cognitive users.