Abstract: A dynamic model of involute gears with asymmetric teeth was proposed based on the analysis of mesh characteristics when the gears transmitting. The numerical integral and numerical simulation method were used to study nonlinear vibration. Considering the time-variant mesh stiffness when the gears transmitting, the vibration characteristics were compared between gears with symmetric teeth and with asymmetric teeth. The results showed that under the same condition the gears with asymmetric teeth had better dynamic characteristics than those with symmetric teeth.