The Synchronizer is an essential part of the manual transmission. The basis for the synchronizer optimization is provided by studying the influence of the synchronizer shift sleeve parameters on shifting performance. The 3D model of synchronizer is established by using UG and simulated in ADAMS. Then the accuracy of the model is verified according to the simulation results and the theoretical results. The optimal range of the shift sleeve Mei angle and the influence law of the change of the positioning ball groove angle of shift sleeve on synchronization time and shifting resistance which caused are got through the analysis of the synchronization theory.