Abstract: Some subway vehicles will generate abnormal low-frequency shaking during operation. In order to explore the reasons, we will track and analyze each vibration mode of the vehicle system. According to the definition of European pasting schedule, we will track the rules of the speed's change of each mode, automatically recognize and track similar vibration models in the process of tracking. When two similar mode shapes vibrate together, resonance will occur, resulting in vehicle shaking phenomenon. Coupling degree is put forward to judge the strength of resonance. When the coupling degree is large, the resonance phenomenon is obvious. On the other hand, in order to reduce the coupling degree, the vehicle modal resonance can be reduced by optimizing the relevant parameters of the vehicle, so as to achieve the phenomenon of low frequency abnormal rocking of the vehicle.