Abstract: In order to reduce the impurity rate and loss rate in the process of buckwheat cleaning, improving the mechanical harvesting performance of the combined harvester. The single factor tests based on crank length, crank speed, inclination angle of upper screen surface and lower screen surface, swing angle of screen surface, wind direction of fan and fan speed were carried out on the grain cleaning test bench. The orthogonal test and analysis were carried out on these 7 factors at 3 levels. The test results showed that the inclination of upper sieve surface, crank speed, crank length and fan speed had significant effects on the cleaning loss rate and the influence degree decreased successively. Fan speed, fan wind angle, inclination of upper sieve and lower sieve had significant effects on grain impurity rate. The significant factors affecting the cleaning time were crank speed, crank length, inclination of upper sieve, and wind speed of fan. The regression models of grain impurity rate, cleaning loss rate and cleaning time were established was established by SPSS data analysis software, and optimized based on genetic algorithm. The optimal parameter combination was obtained as follows: the crank length of 30mm, the crank speed of 231r/min, the inclination of upper sieve of-3. 8°, the fan wind direction angle of 30°, the fan speed of 600r/min, the inclination of lower sieve of-1°, the vibration angle of sieve surface of 5°, and the cleaning loss rate, impurity rate and cleaning time were 1. 59%, 1. 91%, 7. 93s, respectively. Under the optimal parameters, the relative errors between the experimental values and the theoretical values of each evaluation index were 3. 14%, 1. 22% and 3. 24%, respectively, and the optimized results were highly consistent with the results of range variance analysis, which indicated that the optimization of the regression model of cleaning by genetic algorithm was feasible and the optimization results were reliable. The combination of parameters can provide theoretical basis for the design of buckwheat combined harvester and cleaning device.