The impact factor is an important parameter for dynamic analysis of bridge. The reasonable value of impact factor can influence the safety and economy of bridge. Nowadays, numerical simulation has become an important method to study the impact factor. Therefore, the accuracy using numerical analysis to obtain impact factor depends on the reasonable vehicle-bridge coupling vibration analysis, and also depends on the calculation method of the impact factor. As the first steel web-concrete composite arch bridge in the world, the vehicle-bridge coupling vibration from the aspects of bridge model, vehicle model, Rayleigh damping calculation and road roughness simulation of Wumengshan Bridge is analyzed using ANSYS. The two-point method, the three-point method and the new correction method are also used to calculate the impact factor of the dynamic time history curve, and compared with the standard value. The results show that the impact factor obtained by the three methods is greater than that calculated by the specification, which may influence the safety of the bridge.