An improved algorithm based on bidirectional A* is proposed to solve the problem of high-efficiency UAV trajectory planning in 3D complex environment.A sector search area is designed to reduce computation overhead.In order to improve search efficiency,the dynamic weighted bidirectional A* algorithm is developed to optimize cost function.The key node screening strategy is introduced to eliminate redundant points in trajectory and generate global optimal static trajectory.Aiming at the problem of dynamic obstacle avoidance in trajectory,an optimization objective function of the shortest dynamic obstacle avoidance trajectory is designed,and the dynamic obstacle avoidance algorithm based on the calculus of variations with trajectory tolerance constraints is introduced,which realizes online adjustment and optimization of local trajectory.Simulation results show that the designed trajectory planning algorithm can not only plan an expected trajectory of UAV with high efficiency in complex environment,but also dynamically avoid random obstacles.