Abstract: 【Objective】 Aiming at the phenomenon of high grain breaking rate and entrainment loss caused by space blockage and drum failure during corn threshing, this project intends to design a feeding and throwing combined threshing separation device. 【Methods】 The feeding acceleration roller was designed at the feeding entrance of the front end of the drum, and the radius was determined to be 150 mm through the stress analysis of the ears and straw, and the rotating speed was determined to be 430 r/min based on the rake line speed of the cross-bridge conveyor chain and the corn threshing speed. By analyzing the type of drum working section, the angle of the guide plate in the guide hood was optimized to be 30° in feeding section, 20° in threshing section and 10° in separating section. A litter throwing device was designed and installed at the straw discharging outlet at the back end of the roller, including a straw discharging roller and a straw discharging concave plate. A three-factor and three-level field orthogonal experiment was designed with rotating speed of roller, gap of concave plate and feeding amount as experimental factors, and grain breakage rate and unstripped rate as evaluation indexes. The test results were analyzed by the trend of response surface among the factors, and the data were optimized by Design-Expert 12 software. 【Results】 The orthogonal test results showed that under the conditions of roller speed 447.11 r /min, concave clearance 34.74 mm and feeding amount 16.14 kg /s, the grain breakage rate reached 2.68% and the uncleaned rate reached 0.99%. 【Conclusion】 Field verification experiment shows that: Under the conditions of cylinder speed 450 r/min, concave clearance 35 mm and feeding amount 16 kg/s, the average grain crushing rate reaches 2.73%, the average unpeeled rate reaches 1.05%, and the relative error between the test results and the optimization results is within 5%, which has proved that the device design is reasonable, superior to the traditional threshing separation device, thus meeting the national threshing standard.