Abstract: Aimed at the problem of high cleaning loss rate, impurity rate and secondary impurity rate due to improper adjustment of main operating parameters of wheat combine harvester double-outlet multi-dults cleaning device, single factor and multi-factor optimization tests that took feed amount, wind door opening, fan speed, upper and lower wind deflector angles as main test factors were conducted. The influences of each test factor on the cleaning loss rate, impurity rate, and secondary impurity rate were studied to find the optimal parameter combination. Firstly, referring to the relevant parameters of Kubota 988 model, which has a large amount of wheat harvester in the market, a test-bed with double air outlet multi-ducts for combine harvesters was built. When there were four ducts, the wheat cleaning loss rate 0.78% and impurity rate 0.48% were the lowest compared to the two or three ducts. Moreover, through single factor test of double air outlet four ducts cleaning device, the optimal range of feed amount was determined from 4.5 to 5.8 kg/s, wind door opening was 0°-20°, fan speed was 1 200-1 600 r/min, upper and lower wind deflector angles were 0°-20°. The results of single factor test showed that the cleaning loss rate increased with the increase of the feed amount and fan speed, and decreased with the increase of the upper and lower wind deflector angles; the impurity rate decreased with the increase of fan speed, and increased with the increase of the feed amount and upper and lower wind deflector angles; the secondary impurity rate increased with the increase of feed amount, and decreased with the increase of the wind door opening, fan speed and upper and lower wind deflector angles. The multi factor bench test and the orthogonal test with five factors and three levels were carried out by using the Box Behnken center combination test design theory. The regression equations about the cleaning loss rate, impurity rate and secondary impurity rate were obtained. The results showed that the factors of fan speed, feed amount, upper wind deflector angle had significant impact on the cleaning loss rate, the factors of fan speed, upper and lower wind deflector angles have impact on the impurity rate, and the factors of upper wind deflector angle, the fan speed and the feeding amount have significant influence on the secondary impurity rate. Through optimization of the target parameters, the optimal parameters combination were the feeding amount 4.5 kg/s, the wind door opening 10.2°, the fan speed 1 548 r/min, the upper and lower wind deflector angles 20° and 0°, at this time, the cleaning loss rate, impurity rate and secondary impurity rate were 0.79% , 0.40% and 0.82% respectively. Furthermore, the bench test under the optimal parameter combination condition was carried out to verify the accuracy of the optimal results. The results of bench test showed that the cleaning loss rate, impurity rate and secondary impurity rate were 0.75%, 0.38% and 0.76% respectively, and the error between test results and optimization results were 5.1%, 5.0% and 7.3% respectively. The results of this study can provide the references for the adjustment operating parameters and technical support for improving the performance of the multi-ducts cleaning device of the combine harvester.