With the development of China's aquaculture industry, the requirements for mechanization and intelligence in the field of aquaculture processing have been increasing. A roller fish grader with adjustable parameters was designed for the problems of less research and application of fish grading machinery and low efficiency of manual grading in China. The single-factor and multi-factor response surface tests of roller speed, diameter and inclination angle on grading accuracy were carried out by EDEM simulation. The effects of roller parameters on the accuracy of fish grading were analyzed to optimize their working parameters. The results showed that roller speed, dip angle and diameter all had significant effects on grading accuracy, among which, there were interactive effects between roller speed and dip angle as well as the speed and diameter, and the highest grading accuracy was achieved when the grading roller speed was 3.4 r/s, dip angle was 7.8° and diameter was 2.68 mm, with an accuracy of 90.5%. This paper provides a reference for the application of EDEM simulation method in the field of aquatic machinery, and provides new ideas for the design and optimization of fish grader.