Abstract: The phenomenon of abnormal carbody jitter during operation of a type of EMU is analyzed. The evolution law of wheel tread wear characteristics and wheel/rail contact relationship in reprofiling cycle is grasped.The evaluation relation of wheel equivalent taper and tread concave wear is proposed.The influence of wheel tread concave wear development on vehicle stability is studied by establishing a rigid-flexible coupling vehicle dynamics model.Results show that with the increase of train wheel tread concave wear, the contact range between wheel and rail becomes narrower, and the contact point jump phenomenon is easily occurring. Meanwhile, the wheel tread equivalent taper also increases, and the critical speed of vehicle will decreases significantly, lowering train operation stability. Therefore, when there is a relatively large excitation on the line, the abnormal vibration of the carbody may occure in the condition of a large equivalent taper. The wheel-rail mat-ching relationship can be improved through wheel tread reprofi-ling,which solves the problem of abnormal vibration of EMU.