Abstract: Abstract: Problem Statement: The rape plant area is the largest in oil-bearing crops in China and accounts for a quarter of the total rape plant population in the world. However, uneven maturity of this rape limits the development of rape harvest mechanization. Currently, most researchers focus on a threshing and separating device known as a single-axial cylinder, the characteristics of which include short separating process duration, high harvest loss, and high trash content in the seed container. On the other hand, multi-cylinders, which are also threshing and separating devices, have advantages such as less damage to seeds and better performance in threshing and separating with long separating duration, large separating area, large concave drum gap and low speed. Thus, it is essential to study the optimal structure and operation parameters of the multi-cylinder threshing and separating devices. Approach: In order to obtain the optimal structure and operation parameters of the multi-cylinder threshing and separating devices for combine harvesters, comparative tests were carried out on a test bed. One combination was a tangential-horizontal axial flow (two cylinders: the first a tangential flow cylinder and the second a horizontal axial flow cylinder). The other was a tangential-horizontal-horizontal axial flow (three cylinders: the first a tangential flow cylinder and the second and third horizontal axial flow cylinders). The tests were conducted separately for both combinations using different feed rates, cylinder speeds, concave clearances, and tooth threshing bars. The test bed was subject to modularization. The tangential flow cylinder and horizontal axial flow cylinder were relatively simple to assemble and disassemble. The torque-speed sensors (Westzh Company, Type CYB-803S, Accuracy ±0.5% FS) were installed into the driving shafts of the threshing cylinders. The structure parameters and operation parameters were adjusted and the linear velocity of the conveyor belt, rotational speed of each cylinder, and torque were recorded in Computer. The axial distribution of the seed, MOG (other-than-grain), power consumption of each cylinder, and loss rate were examined through the use of an orthogonal experiment. The distribution of threshed material was tested and analyzed, and the threshing loss of the experiment was acquired using the Visual Analysis Method, and the corresponding power consumption of each cylinder was calculated. The optimal structure and operation parameters of the multi-cylinder threshing and separating devices were obtained through the comparison of threshing loss and threshing power consumption of the two combinations. Results: After a comparison of the threshing rate and threshing power consumption under the same conditions was conducted, it was found that the use of the tangential-horizontal-horizontal axial flow device was far better than that of the tangential-horizontal axial flow device. The experiment results indicated that the quality distribution of seed and MOG under the first and second threshing and separating cylinder were similar in both combinations of tangential-horizontal axial flow and tangential-horizontal-horizontal axial flow, and that the quality rate of seed to MOG was near to 1 under the first cylinder. Based on the analysis of the orthogonal experiment, the feed rate and drum speed were found to be the major factors that influenced the loss rate. Conclusions: Optimal combination of minimum loss rate was obtained from the tangential- horizontal-horizontal axial flow threshing device with a feed rate of 1.8kg/s, speeds of 800, 850, 900r/min and concave clearance 20, 25 and 30mm for the tangential cylinder, the first horizontal cylinder and the second horizontal cylinder, respectively, and 3-row spike.