Aiming at the problem of secondary impact in the process of synchronizer shift, the mechanism of impact was analyzed, and the simulation model of synchronizer shift was established by AMESim software. The influence of tooth width, locking angle, tangential clearance and back angle on the shift impact of synchronizer was analyzed. Three shift impact evaluation indexes of shift time, secondary impact force peak and shock extent were proposed. Orthogonal test and variance analysis were introduced to screen out the tooth profile parameters that had significant influence on shift impact. The response surface approximation model of the evaluation index was obtained by the full factor test, and the optimal level scheme of the tooth profile parameters was determined. The results show that when the tooth width and locking angle increase, the shift impact decreases significantly, and the tangential clearance and back angle have little effect on the impact. When the tooth width is 4.2 mm and the locking angle is 36°, the shift impact is the smallest.