In the transmission system of drive axle, the gears' transmission performance of final drive and differential is the key to transmission system. Based on Automatic Dynamic Analysis of Mechanical System (ADAMS), the virtual gear meshing prototype of final drive and differential were established. Based on the Hertz elasticity impact theory, the contact forces between gears were built. The real-time dynamic simulation of gear meshing was achieved. The gears’ transmission of final drive and differential in drive axle was simulated under limit conditions by imposing different torque in driving gear of final drive and differential gears. The curves of meshing force and angular speed of differential gears and driving gears of final drive are obtained. The theoretical reference is provided to the study of the dynamic characteristics in gear transmission system.