Taking a China high speed EMU as an example, the dynamic computer model was established based on the SIMPACK software, vertical damping and rubber joint stiffness of first stage vertical damper were chosen as variables, further its impact on the EMU stability, stability and safety was analyzed. Simulation results show that: the stiffness of rubber joints of a vertical damper has no obvious influence on vehicle stability，but with the increase of vertical damping, the critical speed increases；when the stiffness of the joint is greater than 5 MN/m, the stiffness has little influence on the vehicle stability；with the increase of vertical damping, the stability is slightly improved；the influence of joint stiffness and vertical damping on vehicle safety is not large.