Abstract: The hierarchical optimization method is proposed to deal with the multiple cooperative UAVs mission planning problems. First, the flight paths of multi-UAVs in executing each task are planned in virtue of the Dubins curve and B-spline curve. The costs of planned flight paths are used to estimate the costs of tasks. The task assignment problem is therefore solved as a Multiple Bases Multiple Traveling Salesmen problem. Second, the Gauss Pseudo-spectral method is used to generate the optimal trajectories of UAVs. To improve the computation efficiency, the generated flight paths in the first layer are used as the initial solution of the optimization problem. The proposed method is demonstrated by numerical simulation.