Abstract: Aiming at the global optimization problem of the static path planning of the autonomous unmanned watercraft on the surface，we propose a global path planning method based on an improved heuristic function to enhance the accuracy of the global path planning algorithm. The grid method is used to model the known environmental topographic map. This paper designs a new heuristic function based on the A^* algorithm. It optimizes the path by changing the gain coefficient of the navigation controller. Because the drifting effect of water surface obstacles will affect the path planning of the autonomous unmanned watercraft on the surface，the drift increment caused by the drifting effect of the water surface obstacle is simulated by setting different obstacle shapes and sizes. The MATLAB simulation platform is used for many experimental tests，and the test results prove the actual reliability of the improved obstacle avoidance strategy algorithm.

Key words: global path planning, heuristic function, obstacle avoidance strategy, autonomous unmanned watercraft on the surface