The movement characteristics of rice are important indicators to explore the optimal threshing area and threshing force. This paper presents the motion parameters for threshing straw in the tangential and axial threshing units of the combine. Through the study of the optimal threshing area and threshing force, the reasons for the non-threshing of grains were obtained, which provided the basis for the design of the longitudinal and axial threshing drum. By comparing the threshing force and the detachment force of the grain stem, stem branch and branch axis, the threshing ability of each part of the longitudinal and axial threshing drum was obtained. The results showed that the separation force ranged from 1.48N to 2.29N. The straw performs approximately periodic helical motion in the axial threshing device. The grains on the ears are threshed by the ears of 1-6 rows of longitudinal and axial threshing drums. 2-3 rows of beaters produce stalked grains, and the optimum threshing force is 2.06 N-2.15 N to ensure threshing without stalks and branches. The research is of great significance to explore the optimal threshing zone and threshing parameters.