Aiming at the safety and smoothness problems of path planning for Unmanned Surface Vehicle (USV) in complex marine environment, a multi-directional A ^* path planning algorithm was proposed for obtaining global optimal path. Firstly, combining the electronic chart, the rasterized environment information was established, and a safe area model of USV was established according to the safety nevigation distance constraint. And the A ^* heuristic function with safety distance constraint was designed based on the traditional A ^* algorithm to ensure the safety of the generated path nodes. Secondly, a multi-directional search mode was proposed by improving the eight-directional search mode of the traditional A ^* algorithm to adjust the redundant points and inflection points in the generated path. Finally, the path smoothing algorithm was used to smooth the inflection points to obtain the continuous smooth path that meets the actual navigation requirements. In the simulation experiment, the path distance planned by the improved A ^* algorithm is 7 043 m, which is 9.7%, 26.6% and 7.9% lower than those of Dijkstra algorithm, traditional A ^* four-directional search algorithm and traditional A ^* eight-directional search algorithm. The simulation results show that the improved multi-directional A ^* search algorithm can effectively reduce the path distance, and is more suitable for the path planning of USV.