Abstract: To solve the wheel wear problems of the subway vehicles such as wheel tread wear, spalling, wheel out of round, and the problem that the vertical vibration of car body and the vertical ride index exceed the standard values, the additional stiffness function of the traction bar was studied through theoretical structure analysis and dynamic simulation. The results show that the vehicle braking system was not the main cause of the above problems, and that the additional stiffness function caused by the short length of the traction bar and the bigger connection stiffness on the ends are the main reason why the car body is sensitive to vertical impact. For the vehicle in braking condition or running on curve, the damping function of the secondary suspension decreases due to the additional stiffness of the traction bar system. The response of the car body to the vertical impact increases significantly if the additional stiffness function of the traction bar system is taken into account. The vertical dynamic response and vertical dynamic performance of the subway vehicle can be improved efficiently by decreasing the connection stiffness of the traction bar to 25%.