In order to solve the obstacle avoidance problem of UAV in complex environments,a UAV dynamic path planning algorithm based on improved Bi-RRT and DWA is proposed.The Bi-RRT algorithm is improved by setting heuristic function,dynamic step size and safe distance to improve the search efficiency and safety of the global path.Then,the redundant road sections in the path are trimmed,and the optimal global path is obtained by interpolation and smoothing operations on the trimmed path.The obstacle distance evaluation function is modified and the target distance evaluation function is introduced to improve the accuracy of the score of the predicted local trajectory.Then,the velocity command is output in real time to control the UAV to track the optimal global path and realize local dynamic obstacle avoidance.The simulation results show that the path generated by the improved Bi-RRT algorithm is shorter and smoother with higher safety and less planning time.In the complex environments with both dynamic and static obstacles,the proposed fusion algorithm can control the UAV to accurately track the optimal global path and efficiently complete local dynamic obstacle avoidance.