UAV path planning is the most important and most complex part of UAV mission planning.Because particle swarm algorithm is easy to fell into local optimal solution and “premature”, and the precision of planning flight route is low, a parallel implementation of two-swarm particle swarm algorithm for route planning is presented, this algorithm is comprised of two particle swarm algorithms which have reverse direction of search, and this algorithm can extend the range of search through cooperation of two particle swarm algorithms, overcome the problem of falling into local optimal solution and improve the precision of flight route. With unexpected threat detected in flight, UAV will search near point of flight route and then replan route from this point to target point.Simulation results show the effectiveness of the algorithm.