Aiming at the two-aircrafts cooperative cross-positioning task to improve the precision of direction finding and solve the problem of path planning. By analyzing on circular probability error（ CPE） of the two-aircrafts cross positioning and the dynamics constraints of the UAV

a 3D path planning model for two-aircrafts cross positioning is established

and a particle swarm optimization（ PSO） algorithm with constraints is introduced to dynamically plan the path of the UAV

so as to improve the precision of direction finding and realize automatic control. The simulation results show that the PSO algorithm can effectively plan the path of the UAV and continuously improve the precision of the direction finding. The algorithm has high timeliness and has certain practical application value.