In this paper, a screening machine was designed to remove the impurities in the tuber harvest, which integrates the functions of vibration screening, air separation, and flexible polishing. Discrete element simulation analysis was carried out to investigate the movement of tuber harvest and soil in the machine and the effect of polishing and removing impurities, the rationality of the structure, and the size were verified. Orthogonal tests were designed and carried out, with the rate of impurity, loss, and crushing as indicators and crank speed, impeller speed, and polishing roller speed as factors. The optimum working parameters were obtained: crank speed 280.12 r/min, impeller speed 1056.27 r/min, polishing roller speed 405.02 r/min, the impurity content was 0.29%, the loss rate was 1.01%, and the breakage rate was 0.11%. Through experimental verification, the actual value and theoretical value are basically the same, which verifies the rationality.