The Northwest Pacific saury (Cololabis saira) separating system mainly consists of the fish and water separator and the fish size grader. Studying on the separating system and raising some improvement measures are beneficial to reducing the labor costs, improving the grading effects and productivity. Aiming at the traditional separating system, the main structure, box structure, seepage plate structure of the fish and water separator and the separating structure, stand bar structure of the fish size grader were redesigned based on the fishing experience. The improvement measures are described as follows: (1)constructing a drainage channel below the main structure of the fish and water separator, and the angle between drainage channel to the horizontal plan is about 15~20 °; (2)constructing a top cover above the fish and water separator box, and adhering a layer of flexible waterproof thermoplastic elastomer (TPE) to the inner cover layer of the box and the top cover; (3)The seepage plate is designed into a removable twotier board structure; (4)The number of the sorting pipes increased to 15, and the length increased to 250cm, the grading storages are added up to five; (5)The original fixed stand bars of the fishing separator are redesigned into removable stand bars; (6)Fish skateboard is designed to slope about 30 °; (7)adding a set of water jet screens over the fish separator. The redesigned fish separating system is suitable for the separating of Northwest Pacific saury and the other smallsize fish species.