In order to make Unmanned Surface Vessel in complex sea conditions automaticly and safely avoid dynamic obstacles,a algorithm of automatic collision avoidance based on Velocity Obstacles and considered USV maneuvering characteristics is presented. Firstly, the relative velocity is calculated by USV and avoidance objects’ ground speeds,and then the angular relationship between their relative velocities and positions is analyzed and determined, drawing a feasible avoidance path range，by changing  the direction of navigation to complete the dynamic obstacle avoidance. Simulation results indicate that: the method effectively overcomes the limitations of local path planning, and more in line with actually sailing and avoiding collision of maneuvering requirements, enabling USV security avoidance with multiple dynamic obstacles in complex environment.