为解决无人艇自主避障中感知系统测得的障碍物信息不稳定问题，提出一种符合国际海事避碰规则（COLREGS）面向不稳定障碍物的改进速度障碍算法（Improved Velocity Obstacle, IVO），算法利用最小会遇时间、距离自适应阈值来优化避障状态判断；使用滑动窗口以及前视视线解决无人艇因障碍物信息不稳定导致在进入和退出避障状态时的边界跳动问题；通过设置角度缓冲区降低了避障中避碰规则的频繁切换.最后，在自主开发的无人艇半物理仿真系统中与传统VO算法进行了对比，结果表明，IVO算法在边界判断和避障稳定性上较传统方法更有优势，证明了算法的有效性和可行性.

An improved velocity obstacle (IVO) algorithm for unstable obstacles was proposed for the autonomous obstacle avoidance of unmanned surface vessels (USV) with unstable obstacles , which conformed to the Convention on the International Regulation for the preventing Collision at Sea (COLREGS). The algorithm used the adaptive threshold of minimum encounter time and distance to optimize the judgment of obstacle avoidance state. The sliding window and forwardlooking line of sight were used to solve the problem of boundary jumping when entering and exiting the obstacle avoidance state due to the instability of obstacle information. The frequent switching of collision avoidance rules in obstacle avoidance was reduced by setting angle buffer. Then, the IVO algorithm was compared with the traditional VO algorithm in the selfdeveloped USV semi physical simulation system, and results show that the IVO algorithm has more advantages in boundary judgment and obstacle avoidance stability than the traditional methods, which proves the effectiveness and feasibility of the proposed algorithm.