Four mathematical models of oil film pressure, contact force of asperity, axial force of synchronizer ring and cone torque are established by means of average Reynolds equation and asperity friction principle. The coupling number of oil film thickness and speed difference of synchronization is solved by using 4-Runge-Kutta method. The changing rule of oil film thickness, speed difference, viscous torque, asperity friction torque and total torque are analyzed. After verification of the mathematical model of synchronization, the effects of structure factors such as the width of synchronizer ring, radius of synchronizer ring, cone angle and thickness of friction material of synchronizer are studied by the model. The results show that the increase of the width of synchronous ring results in increasing viscous torque and asperity friction torque, decreasing the decline rate of oil film thickness, the response of asperity friction torque is delayed and the synchronization time is increased. With the increase of the radius of synchronous ring, the viscous torque and asperity friction torque increase, the oil film thickness descends and the synchronization time is shortened. When the friction angle increases, the viscous torque increases, the asperity friction torque decreases, the speed difference descends slowly and the synchronization time prolongs. With the increase of friction material thickness, the asperity friction torque and the changing rate of oil film thickness increase correspondingly, but the minimum oil film thickness and the synchronization time decrease.