China is the original country of Chinese milk vetch (Astragalus sinicus L.), and also the country with the earliest utilization and cultivation of Chinese milk vetch and the largest planting area in the world. Chinese milk vetch, also known as grass seed, Ziyunying and so on, is one of the main winter green manure crops in paddy fields of central and southern China. To enhance the machanization level of separating and cleaning of Chinese milk vetch combine harvest material, according to the complex component compositions and small difference confounding characteristics of Chinese milk vetch combine harvest materials, the operation mode of “screening first, and then air flow cleaning” was put forward, and a separating and cleaning machine for Chinese milk vetch combined harvest material was designed. Through design selection and parameter calculation of key components of the prototype, the important working parameters of the feeding hopper outlet material layer thickness adjustment mechanism, the screening device and impurity-collection and dust-removal device were determined. Based on the DEM-CFD coupled numerical simulation method, the reasonable value ranges of the main influential factors, such as the material layer adjustment thickness, the vibration amplitude of the screening device, and the air volume adjustment handle gear of the impurity-absorbing duct were confirmed, an orthogonal experimental design was conducted by using Minitab, with the grain cleaning rate and the total entrained loss rate as the response values, the optimal parameter combination that affected the operation quality of separating and cleaning machine for Chinese milk vetch combined harvest material was obtained. The prototype field validation test showed that, when the material layer adjustment thickness was 16.8mm, the screening device vibration amplitude was 35mm, and the air volume adjustment handle gear of the impurity-absorbing duct was 5, after the operation of separating and cleaning machine for Chinese milk vetch combine harvest material，the average grain cleaning rate was 98.07%, and the total entrained loss rate was 2.96%, the experimental results met the design requirements of operation machine.