Abstract: The nonlinear dynamics of a vehicle suspension system with piecewise linear viscous and dry friction damping was studied. The theoretical method on the stability analysis of a system in periodic motion was presented. And numerical simulation was performed to investigate the responses of the vehicle suspension system to harmonically excited vibration with respect to different combinations of the damping parameters. The stick-slip vibrations induced by dry friction were analyzed in detail as well. As the results, it was favorable to decreasing the responses amplitude of the system to vibration by increasing the friction force. However, the complicated stick-slip vibration took place at a small velocity, which led to a severe instantaneous stiff impact load between the wheel and rail. It was suggested to decrease such an instantaneous stiff impact load by supplementing elastic suspension between the wheelset and side frame.