Abstract: Due to the fact that the electric vehicle equipped with automatic mechanical transmission (AMT) cancels the clutch, a higher inertia of the synchronizer input end increases the secondary impact of gear engagement. The gear engagement process of the synchronizer was divided into seven phases, and the dynamic analysis of the gear engagement process was conducted. The results of theoretical analysis and experimental validation show that the rapid increase of the axial speed of synchronizer sleeve during the second free movement stage is the main reason for the excessive secondary impact. Reasonably reducing the average voltage applied to the gear shifting motor during the synchronization phase can effectively reduce the secondary impact of gear shifting, under the premise that the gear shifting duration is not increased much.