Abstract: With the continuous improvement of train speed, the effect of the mass, the moment of inertia and the elasticity of the wheelset in the wheel-track vibration system is increasing and can not be ignored any more. By using the assumed mode method, a mode function of axle with a concentrated mass and a concentrated moment of inertia is obtained, which is compared with the straight beam’s vibration mode function. Based on which a vehicle system dynamic model is constructed, considering the rigid body motion and elastic modes of the axle. By numerical method we got the force, vertical acceleration and the acceleration power spectrum density(PSD) of the rail-wheel coupling system, concentrated mass and moment of inertia Comparing to former researches, th

Key words: concentrated mass;assumed mode method;model function;power spectrum density(PSD);rail-wheel force