The goal of flight path planning is to plan an optimum flight path that can meet restrictions according to flight mission. It is a key technology in the attack and defense of UAV. Because of the complexity of the flight path planning, a new hierarchical path planning approach is proposed. The approach is composed of three steps. The first step is to generate the initial path according to the voronoi diagram. The second step is to evaluate flight paths on a basis of all the restrictions. The last step is to obtain the optimal solution by using the discrete particle swarm optimization (DPSO) algorithm. The simulation shows that the approach has extensive prospect because of its high efficiency and less memory space.