Abstract: For the problems of the heavy grain losing and huge power consuming in crops threshing and separating by China-made tangential-axial combine harvester, the tangential-threshing drum, assisted-feeding drum and longitudinal- axial-threshing drum taking from the tangential-axial combine harvester were used to establish a tangential-longitudinal- axial threshing-separating test-bed in the laboratory. The evaluating indicators of threshing and separating power consuming, and entrainment losing rate and unthreshing losing rate were obtained by threshing and separating performance on the test-bed with the wheat feeding rate of 7.5 kg/s. The threshing and separating power consuming, and entrainment losing rate were converted into complex amplitude indexes to establish the feasible region of the best threshing and separating performance indexes. The experiments showed that the optimal results of wheat threshing and separating were as follows: the total grain losing was 0.56%, power consuming was 66.64 kW, the optimal threshing and separating performance indexes was 0.8935 with the conditions of that the wheat feeding rate of 7.5 kg/s, and the liner speed of the tangential-threshing drum was 21.66 m/s, the threshing components of the tangential-threshing drum was knife tooth, the clearance between the Inlet/Outlet was 30/20 mm, the liner speed of the longitudinal-axial-separating drum was 19.63 m/s, and the threshing components of longitudinal-axial-separating drum was spike tooth and the gap of the threshing was 20 mm.