Using reasonable and efficient autonomous technology for path planning can effectively improve the safety of ship navigation and can reduce human errors of maritime accidents. The planned path by A* algorithm is flawed with broken lines, many turning points and numerous transitional frequencies under the environment modeled by grid method. Smoothing A* algorithm is adopted to delete the removable points which prolong the planned path length. After all the realities of ship navigation are taken into account, smoothing A* algorithm is applied to resolve safe navigation problem for the ship. With the proposed smoothing A* algorithm, simulation results show that the conflict-free path can be planned for ships under different circumstances with static and dynamic obstacles and abide by the COLREGS.