In the cognitive sensor networks, a novel frame structure is proposed based on the cooperative spectrum sensing. In this novel model structure, the cognitive nodes’ (CNs’) spectrum sensing and the data transmission can be conducted simultaneously, and the throughput of the CSN is improved through the optimization of sensing bandwidth. Thus it can be seen that the CNs’ delay QoS (Quality of Service) constraint has an effect on the throughput, and the maximum throughput and the minimum transmission delay cannot be obtained simultaneously. This paper proposes an efficient iterative algorithm to jointly optimize the sensing bandwidth and the decision threshold of the fusion center that the throughput is maximized while the delay QoS constraint is satisfied. The simulation results show that the CSN’ throughput can be improved by using the proposed optimization scheme, and different transmission delay QoS requirements have different values of optimal sensing bandwidth.