In order to improve the mechanization and automation level and accuracy of the soybean plot test, aiming at the bottleneck problem of soybean plot seeder cleaning and replacing technology, a kind of threeleaf type airsuction seed meter with automatic clear and replace seeds features for soybean plot test was designed. The motor was used as the power source to drive the gear seed plate and the threeleaf auxiliary seed filling and cleaning and replacing mechanism to quickly complete the nonstop seed cleaning, seed replacing and seed filling between neighboring plot. The basic structure and working principle of the seed meter were described, and key components were theoretically analyzed to determine the structural parameters based on the requirements of the breeding test. Combined with the requirements of breeding test, the structural parameters were determined through theoretical analysis of key components with the spatial analysis principle of TRIZ theory. The EDEM virtual simulation of the threeleaf auxiliary seed filling and cleaning and replacing mechanism was performed to analyze the auxiliary seed filling process and determine the blade inclination angle of the best auxiliary seed filling effect. According to the agronomic requirements of community breeding, a threefactor fivelevel quadratic orthogonal rotation center combination test was carried out, and the working speed, vacuum degree, and cleaning and replacing seed time were taken as test factors, and the eligibility index, replay index, missed index, and cleaning and replacing distance were selected as the test indicators. The result showed that when the optimal parameter combination was as follows: working speed was 5.3km/h, vacuum degree was 4.6kPa, and cleaning and replacing seed time was 0.3s, the eligibility index was 95.29%, replay index was 3.29%,missed index was 1.42%, and the cleaning and replacing distance was 554.6mm, which met the sowing requirements of soybean plot test.