Abstract: An improved RRT^* algorithm is developed to accelerate the planning process and achieve shorter ship sailing distance. The target point is expended with offset to transform the problem concerning a target point into a problem of target area and a feasible path is calculated as the preliminary path. This preliminary path is used to define a new sampling area. The processis repeated to produce the feasible path plan proposal. The proposed path plan is optimized through pruning and cubic spline interpolation and a smoothed path plan good for ship navigation is generated. The final path plan is checked through simulation in PyCharm.Tests proves that the improved RRT^* algorithm converges faster and generates shouter path than original RRT^* algorithm does.