With respect to the problem of 3D path planning of Unmanned Aerial Vehicles (UAV) under uncertain environments when the target is movinga method of fast 3D path planning was designed based on the improved D*Lite algorithm.By use of the improved cost evaluating function and the realtime information of unanticipated threats and moving targetsand based on the constraints together with the improved search algorithma method of 3D path planning for UAVs was given.The simulation results demonstrated that the algorithm can not only meet the realtime path planning demandsavoid the unanticipated threats and attack the moving targetsbut also reduce the search spaceimprove the search efficiency and optimizing capabilitywhich is a good method for path planning of UAV under uncertain environments.