Abstract: To solve the optimizing problem of rapidly-exploring random tree algorithm (RRT), a cyclic optimizing RRT algorithm is proposed. By introducing path length constraint into RRT algorithm as heuristic condition, useless points in search space are exterminated, near optimal path can be obtained. By introducing path length constraint of planned feasible path into next algorithm execution as heuristic condition, useless points in search space are exterminated through cyclic iterative strategy， path length is shortened after each operation. The near optimal path will be found after multiple operations, then the problem that the basic RRT algorithm for UAV path planning is overcome, path length constraint as heuristic condition sufficiency is used， meanwhile, a series of feasible alternative path are obtained, they can be quickly chosen through cooperative arrival time in coordination mission. Simulation results demonstrated that this proposed method can fast get safe and near optimal path that takes into account the dynamic constraints of UAV.

Key words: unmanned aerial vehicle (UAV), rapidly-exploring random tree, path length constraint, cyclic iteration