Because of the complex vibration caused by various excitations， the transmission is not only related to driving comfort， but also has an important influence on the life and reliability of the transmission system. Considering the excitation source of the transmission and the mode of internal parts and external shift control can effectively improve the vibration problem of the transmission in the early design and development stage. Through a case analysis of mechanical transmission gear early abnormal wear and tear caused by the shifting handle jitter， it is deduced that the shaft assembly and balance block are resonant due to the excitation of the main reduction gear based on the vibration characteristics. The improvement strategy are proposed and verified by experiments.