According to simplified model of UCAV launching area, the attack trajectory decision-making for UCAV is introduced. A hierarchical trajectory-designing approach is proposed, and the problem is changed into optimization design. Firstly, the original trajectory is created by Voronoi diagram based on the known flight environment. Secondly, attack trajectory decision making model of UCAV is built based on attack trajectory constraint conditions, flight distance model and threaten model. And the discrete particle swarm optimization is presented to solve it. The simulation results show that DPSO algorithm is simple and can be used to effectively solve the problem of attack trajectory decision-making for UCAV.