In order to understand the throttling characteristics and the damping force abnormal fluctuations,tests and simulations were carried out on the course of pressure change and the force process acting on valve disc of a hydraulic shock absorber.Setting sub cycle can reduce the amount of calculation,however,it will cause the pressure’s unreal fluctuations.After fitting,the simulated curve of pressure vs velocity with sub cycle setting can represent the velocity characteristics of damping force.For the 118 shock absorber,the throttle orifice decides the throttling characteristics before the valve opens;and the gap between valve disc and piston decides the throttling characteristics after the valve opens.Three obvious layers appear in the stress distribution of the valve disc,so the uniform distribution hypothesis isn’t appropriate.The results show that,the change of contact form between valve disc and its saddle is one of the causes which induce the damping force abnormal fluctuations.