A multi-body system dynamical model including elastic deformation effect of structure is put forward based on the rest results of principal modes of passenger carbody. The influence of the carbody elastic vibration on ride comfort is analyzed numerically in detail. In order to settle the vehicle vibration problems including the elastic deformation effect due to high speed, the method of semi-active suspensions is utilized. The dynamic responses of the high speed passenger car with passive semi-active On/Off damper are studied and compared. The numerical simulation results for the passenger car are validated with a roller test rig.