Abstract: Cognitive radio becomes a promising approach to increase spectrum efficiency, and power and spectrum allocation is a very important part.We use a union matrix instead of the traditional power distribution matrix and the spectrum allocation matrix, maximize the system throughput under the condition of the smallest system total transmit power and interference caused by unauthorized users.We redesign the location and speed of Particle Swarm Optimization (PSO) more suitable for solving the the joint optimization problem.The simulation results show that the algorithm complexity decrease compared with the tradition algorithm, and increase the system throughput.