In view of the industrial aquaculture, it is necessary to classify the fry in different growth stages according to their sizes with high efficiency and accuracy, so as to meet the requirement of separate cultivation, a roller-type fry sorting test prototype was designed. The coupling model of fry-mechanical components was established by using discrete element software. As the working parameters of the sorting machine were used for the experimental factors, and the sorting efficiency and accuracy of fish-dividing were used for evaluation indexes, the simulation results were obtained and verified by experiments. Finally, the single factor and orthogonal influence simulation analysis was carried out based on the established coupled simulation model, and the primary and secondary order for each working parameter and the optimal parameter combination were determined. The results showed that the primary and secondary order of the influence factor for the sorting accuracy was: roller lifting angle, fish intake and roller speed, and the primary and secondary order of the sorting efficiency was: roller lifting angle, fish intake and roller speed. Based on the principle of improving the sorting accuracy and efficiency, the parameters were optimized by Design-Expert 8.0.5 software, and the optimal combination was determined as follows: the roller speed was 138.40r/min, the roller lifting angle was 10.47°, and the fish intake was 3.00 tails/s. The research results would provide an important reference for the optimization design of the following fry grading equipment.