Abstract: Abstract: There is a large land area for potato s in China, the mechanized potato sowing operation is an important part of the entire potato mechanization process. At present, the cultivation mode of potato mechanized sowing is mainly based on cut potatoes, and the uniformity of potato tubers directly affect the quality of sowing. In most areas, manual cutting is still used, and the cutting efficiency is low. In some areas, potato cutting machines are used for potato cutting, which is more efficient, but the traditional potato seed cutting machine cannot get the uniform potato tubers when cutting potatoes, and cannot meet the requirements of mechanized seeding. It would affect the subsequent growth and development of potatoes and has a greater impact on the entire potato mechanization process. Aiming at solving the above-mentioned problem, a grading device that can installed on the potato seed cutting machine was designed. Firstly, the structure of the grading device was introduced, the grading device is mainly composed of grading roller, frame, side baffle, spacing adjustment mechanism, etc. And the working principle of the grading device was explained in the study, the potato seeds inputted in the grading device would be guided and graded with the rotation of the grading rollers, and the small potato seeds would fall from the grading gap of the adjacent grading rollers, while the large potato seeds would continue to move backward with the rotation of the grading rollers until leaving the grading device. Conveyor belts are arranged below and behind the grading device to receive the potatoes outputed by the grading device. Moreover, the cutting process of the potato seeds was explained, potato seeds weighing less than 100 g need to be cut once, and the potato seeds weighing more than 100 g need to be cut twice or more to meet the sowing requirements. The stress state of potato seeds on the grading rollers and the movement state on the grading rollers were analyzed, so as to determine the structural parameters of each part of the grading roller wheel of the grading device and the reasonable grading roller rotation velocity. The number of grading rollers, the rotation velocity of the grading roller, and the feeding amount were selected as the experimental factors, and the grading precision was selected as the evaluation index for the orthogonal test. Kexin 1 was selected as the experimental potato seeds. The software Design-Expert 8.0.6 was used to process and optimize the experimental data and determine the optimum parameter combination. The test results showed the primary and secondary order of influencing factors for the grading precision. The order was the number of grading rollers, the rotation velocity of the grading roller, the feeding amount. And the article performed a verification test on the optimum parameter combination obtained from the test. The verification test was conducted under the optimum parameter combination and the results showed that when the number of grading rollers was 7, the rotation velocity of the grading roller was 110 r/min, and the feeding amount was 40 t/h, the grading precision was 98.7%, which can meet the grading requirements. This research provides a high-efficiency and high-grading precision device for potato seed cutting machine.