To deal with the long time-consuming problem of existing UAV route planning methods, a rapid 3D route planning method based on improved A* algorithm is proposed. This method adopts hierarchical strategy, makes use of an A* search algorithm based on Dynamic Time Warping (DTW) Distance to plan a 2D route firstly. Then, a height planning method based on particle sedimentation algorithm is proposed to plan the 3D route on the basis of the 2D route. To further enhance the real-time planning ability in condition of meeting sudden threat, an online replanning method is proposed. This method adopts large-step A* search to generate a series of guidance points, then uses DTW-path to implement route re-planning. Simulation results show that the proposed method can obtain a feasible path and significantly shorten the planning time.