The straight bevel gear used in differential gear unit for tractor , The rear output bevel gear transmission mechanism of the tractor gearbox, the mechanism includes a rear drive drive bevel gear shaft and a rear output gear shaft arranged perpendicular to the rear drive drive bevel gear shaft. The bevel gear, the rear output gear shaft is provided with a driven bevel gear that meshes with the driving bevel gear, and the shifting gear is sleeved on the rear drive driving bevel gear shaft through a spline, characterized in that the driving bevel gear and the rear drive driving The bevel gear shaft is made into an integral structure. It can not only meet the rigidity requirements of power transmission, but also have a deceleration function, so that the small gearbox set on the rear output transmission assembly of the traditional tractor can be omitted, and the production cost can be reduced..