China is the country of origin of Astragalus sinicus L., and also the country with the earliest utilization and cultivation of Astragalus sinicus L. and the largest planting area in the world. Astragalus sinicus L., also known as Chinese milk vetch, Zi yunying and so on, is one of the main winter green manure crops in paddy fields of central and southern China. Currently, the harvest methods of Astragalus sinicus L.green manure seed are mainly include: artificial harvest and mechanical harvest, artificial harvest is time-consuming and laborious, and the yield of reserved seed for planting is low. Generally, the seed yield of Astragalus sinicus L. in paddy field is 300~650kg/hm2, there are two common ways of mechanical harvest: the first one is segmented harvest, using a rice, wheat, rape or bean swather to harvest Astragalus sinicus L. and then through natural drying, a thresher is used for threshing afterwards, the second one is combine harvest, by adjusting parameters and changing working components of traditional grain harvester or rapeseed combine harvester to complete harvest of Astragalus sinicus L seed. Segmented harvesting process is cumbersome and inefficient, combine harvest is of high efficiency, which is the development trend of Astragalus sinicus L. seed harvest, however, the harvest quality of existing Astragalus sinicus L. green manure seed combine harvester was affected by unreasonable structure configuration of header, weak separation ability of threshing mechanism, and poor impurityremoval function of cleaning device, the loss rate of machine harvest in field measurement was in the range from 31.5% to 32.1%, and the seed impurity rate and breakage rate were high, which seriously affected the scale promotion and application of Astragalus sinicus L. green manure. In order to solve the problems such as poor applicability of header, weak separation ability of threshing mechanism and poor impurity-removal ability of cleaning device during the harvest process of existing-Astragalus sinicus L. green manure seed harvester, a 4LGM-200 type-Astragalus sinicus L. green manure seed combine harvester was designed. The Parameters of the key components, such as the flexible anti pod-dropping seedling-lifting header, the longitudinal rod teeth type threshing device and the air-sieve type layered impurity-controlled cleaning device were designed, the structual parameters (lenth of feeding section, threshin section and grass-dischaging section) of the longitudinal rod teeth type threshing device were determined. Meanwhile, the structural parameters, number and circumferential distribution of threshing elements were designed and calculated. Both the ICEM-CFD mesh partitioning software and Fluent fluid dynamics analysis software were used to perform numerical simulation on the internal airflow field of the threechannel centrifugal fan under the condition when the rotation speed of the fan was 1080r/min and impeller diameter was 385mm, and test verification analysis were carried out as well. Aiming at reducing loss rate, breakage rate and inpurity rate of Astragalus sinicus L. seed during mechanical harvest process, four factors which had a great influence on the harvest quality were selected, including the machine forward speed, rotation speed of the roller, rotation speed of the fan and the scale sieve’s opening. By adoting the Box-Behnken central composite test method, the response surfaces experiments with four factors and three levels were conducted, and then the response surface analysis of the test results was performed by using Design-Expert, through multi-objective parameter optimization, the best combination of working parameters was obtained: the machine forward speed was 3km/h, rotation speed of the roller was 550r/min, rotation speed of the cleaning fan was 990r/min, and the scale sieve’s opening was 35mm. Under these parameters, the field test was carried out, the results showed that the loss rate of Astragalus sinicus L. seed was 2.35%, the breakage rate was 0.22%, and the impurity rate was 0.51%, which was better than the technical requirements of loss rate and breakage rate less than 5% and impurity rate less than 3% specified in relevant standards. 