Abstract:A vertical dynamic model of railway passenger vehicle is built,which covers effects of car body flexibility and all vertical rigid modes.The model is simulated and researched by the control laws of railway vehicle secondary active suspension which are designed according to optimal control theory,based on track irregularity spectrum and time delay between axles.The results show that optimal control of preview based on track spectrum and time delay between axles is more effective than optimal control only based on track spectrum in the aspects of actuator output force and effects of car body vibration control; the acceleration transmissibility from track to flexible car body center can be reduced by optimal control,rigid and flexible vibration also can be controlled; low frequency vibration and the first order bending vibration of car body can be controlled effectively by optimal control simultaneously,but almost no effects on high frequency vibration,the response frequency range of actuator can be selected accordingly.