Research results: Bridge will vibrate with the effects of train dynamic load. The present dynamic design and evaluation are made to the bridges on existing railway lines based on the design speed per hour of train in construction time. After train speeds up, the shock excitation frequency of train changes, along with it the response of bridge structure also changes. After testing，it is found that the main problems of existing bridge are as follows: The univalent lateral natural vibration frequency is over low and the bridge lateral amplitude of vibration frequency is over low and the bridge lateral amplitude of vibration is over large.