Abstract: Abstract: The research on the process of maize threshing, the theoretical analysis and the mathematical modeling have the limitation of ideal hypothesis. The field experiment of whole machine is subject to the system structure or the site and can not be deeply analyzed. Therefore, based on the situation of breeding varieties in Huang-Huai-Hai region, the characteristics of agricultural farming, and the status quo of harvesting machinery, in order to facilitate the study of corn threshing process indoors, with the 4YL-4/5 harvester threshing system, the structural design is optimized, and a tangential flow - transverse axial flow threshing test system is designed. The technical parameters and threshing test scheme of threshing mechanism are studied to reduce the grain broken rate, which is the primary target, and at the same time, we explore the technological potential of the maize kernel harvesting and explore the technical bottlenecks that restrict the industrialization development of maize production in the region. The test bench consists of power system, feeding system, threshing system and auxiliary mechanism, and the structure design is modular, the concave threshing clearance can be adjusted, and different styles of threshing drums or concave plate sieve components can be replaced according to the need, in order to carry out a variety of grain threshing test research. The calibration of the working parameters indicates that the test system can meet the maximum load of 37 kW, and meet the test requirements of the threshing peripheral velocity between 0-29.06 m/s and the feeding amount between 0-8.08 kg/s. Based on the statistical analysis of the biological characteristics of tested maize ear, under the condition that the inlet threshing clearance is 36 mm, the outlet threshing clearance is 12 mm and the feeding amount is 2.6 kg/s, tangential flow feeding drum with spiral tooth structure and transverse axial flow drum with column tooth - plate tooth structure are used to thresh the corn ear with water content of 22%-32%, taking different peripheral velocities of transverse axial flow threshing drum as the test speed. The experiments show that, the threshing capacity of the tangential flow drum decreases with the increase of the moisture content. When the moisture content is below 28%, the threshing capacity of the tangential drum is almost equal to threshing sieving section of the transverse flow drum. When the water content is higher than 28%, the threshing capacity of the tangential flow drum decreases significantly. The grain broken rate index of the threshing system satisfies the national standard of equal to or lower than 5% under the condition of the drum peripheral velocity of 15.84-18.72 m/s and the moisture content of 22%-26%. With the drum peripheral velocity of 17.28 m/s and the moisture content of 24%-26%, the threshing system has the lowest grain broken rate with an average of 1.7%. Through the threshing test system, the theoretical analysis of maize threshing process can be effectively combined with the field experiment, and the related experimental conclusions provide a scientific basis for the design of the corn combine harvester threshing system.