A combined cutting and throwing longitudinal axial flow threshing and separating device was designed to solve the problems like long transport distance and high probability of blockage in threshing device due to the low adaptability of the chain conveyor to rape with high and thick stems in traditional rape combine harvester. The functions of forced feeding, cutting, throwing, threshing and separating were combined, and the key parts of the rape combine harvester were all hydraulically driven to ensure their stepless speed regulation and smooth operation. The structural and working parameters of feeding roller, cutting cylinder and threshing cylinder were determined based on kinematics and dynamics analysis of stem. The orthogonal experiment of cutting cylinder speed, threshing cylinder speed and threshing clearance were carried out while the entrainment loss ratio and power consumption were used as indexes. The results of orthogonal experiment showed that the optimal parameters were 450r/min for the cutting cylinder speed, 450r/min for the threshing cylinder speed and 30mm for the threshing clearance. Under this combination of parameters, the total loss ratio was 0.415%, the mass percentages of short stems in the threshing outlets was 10.43%，the total power consumption for cutting cylinder and threshing cylinder was 4.16kW and the average length of the stems discharged from the outlet of stems was 134.8mm. In addition, the loss ratio and cleaning ratio of cyclone separation cleaning system were 6.13% and 91.97%, respectively. The field experiment showed that the combined cutting and throwing longitudinal axial flow threshing and separating device could realize the uniform continuous conveying, threshing and separating of materials from the header to the threshing device and it could meet the operation demand of the rape combine harvester.