The Chinese cabbage seed market is developing rapidly, and the demand for mechanized harvest is increasing day by day due to the large area and industrial planting. Aiming at the technical problems of low efficiency of artificial harvest and high seed breaking rate by conventional threshing method, a threshing device for Chinese cabbage seed was designed, which was composed of threshing elements such as elastic short-rasp-bar tooth, flexible round head spike tooth and circular tube concave plate. The finite element modal analysis of threshing cylinder was carried out with ANSYS Workbench, and the rationality of structure of threshing cylinder was verified. The feeding amount, cylinder speed and threshing clearance were selected as experimental factors, and the response surface optimization and field comparison experiments were carried out based on the experimental indicators of seed loss rate and breaking rate. Through experiments, the mathematical model between each experiment factor and experiment index was established, the influence of each factor on the index was analyzed, and the structure and working parameters of the device were optimized. The experimental results showed that when the cylinder speed was 726r/min, the threshing clearance was 22.3mm, and the feeding amount was 1.73kg/s, the seed loss rate was 0.68% and the breaking rate was 0.39%.The experimental results met the design requirements, and it can realize the mechanized threshing operation of Chinese cabbage seeds with a low breaking rate during the harvest period.