Mechanization of seed industry is a precondition of seed industry’s modernization, and in order to improve the efficiency and quality of crop breeding, speeding up the development of breeding mechanization is the inevitable trend. For further promoting performance of the team developed cropland plot wheat seeds harvester, also reducing and improving the sample generation harvester which used stripping header to cause the big grain spatter loss, and the threshing unit feeding mouth and its cover internal easily remained and blocked issues, so the 4GX-100 type cropland plot wheat seeds harvester was improved designed. By combining prototype transmission system solutions, the double harvest header and conical threshing unit with telescoping lever were designed, and determined the structural parameter of conical threshing unit(length of feeding section and threshing section, big small section size). Meanwhile, the threshing component structure parameters were designed and calculated, including 〖JP3〗quantity and the circumferential distribution completely. Analyzed of conical roller speed between 406r/min and 610r/min, the length of telescoping lever was 172.5mm and the eccentricity was 40mm. In order to reduce the seed remain rate, the threshing material particle model (wheat grain and short stalks) was established by EDEM software, and carried out simulation analysis of the movement migration process of threshing material in conical threshing unit body. Field performance experiment of the improvement harvester showed that when the prototype feed quantity was 0.52kg/s, the total loss rate was 1.18%, the seed broken rate was 0.13%, the impurity rate was 0.64% and the seed remain rate was 0.02%, and the productivity could reach 0.18hm2/h, which taking only a brief idling could rapidly clear the machine. The machine was in smooth operation, which was no blocking phenomenon in threshing unit feeding mouth and cover internal. The conical threshing unit with telescoping lever could grab, thresh and convey the feeding material, which had strong adaptability, also met the demands of the design and the stipulation of the correlation technique. This study can provide a reference for the development of the cropland plot wheat seeds harvester, and will have a promising prospect of application and spreading in the seed industry mechanization equipment in China.