The IV type COD online speed measuring instrument has discovered and summarized the common problems of foreign online instruments based on nearly ten years of on-site experience. A large amount of manpower and material resources have been invested in thorough improvement, replacing the previous peristaltic pump with a high-precision pump, replacing the single-chip microcomputer with an industrial computer, and replacing traditional manual simulation with a unique process. All of these improvements have completely solved the problems of instability, unreliability, easy blockage and damage of sampling systems that are commonly found at home and abroad.