An improved velocity obstacle method is proposed to improve the ROVs autonomous ability to avoid dynamic obstacles in complex underwater environment.The motion uncertainty of dynamic obstacles in velocity space is transformed into position uncertainty.By analyzing the risk of collision and the velocity obstacle of the maximum expansion circle,the starting and ending time of obstacle avoidance is determined.In order to select the optimal velocity for obstacle avoidance,an objective function considering three factors,i.e.,safety,the tendency of moving towards the target and speed change quantity,is designed.Finally,the feasibility and effectiveness of the method are verified by simulation.