Taking the vibration of rear axle caused by bearing mounting distance of a mini car rear axle main reducer driving gear and driven gear as the research object,in order to optimize the impact of the bearing mounting distance of driving gear and driven gear on the vibration noise,and improve the service life of the bearing of the driving gear and driven gear. The different mounting distance at different speeds are analyzed by simulation respectively by 3D modeling and ADAMS dynamics simulation,the optimal installation distance is obtained,and through the test on the mounting distance,the vibration and noise reduction of the main reducer are greatly improved,and the bearing life is greatly improved. At the same time,it can provide a certain method guidance for the structure design and the vibration and noise of the main reducer of the mini car.