Multi-UAV(unmanned aerial vehicle) cooperative work mode will have important application prospects in future communication. In consideration of the shortage of spectrum resources, this paper establishes a cognitive drone network model, studies the spectrum sensing performance of multiUAV cooperative work, and proposes an optimal fusion criterion to optimize the detection performance. A fast and efficient cooperative spectrum sensing algorithm is proposed to compare the performance of two algorithms under condition of Rayleigh fading and Nakagami fading channels. The simulation results show that: 1) The total error rate of cooperative spectrum sensing can be minimized by using the optimal fusion criterion. 2) The fast cooperative spectrum sensing algorithm can utilize the fewer UAVs for ensuring the detection accuracy of cooperative spectrum sensing, avoiding unnecessary sensing process, reducing the number of secondary users participating in cooperative spectrum sensing, reducing cooperative sensing time, and saving the cost of sensing process. Moreover, compared with the Rayleigh fading channel, this algorithm has better performance under condition of the Nakagami fading channel.