Abstract: The in situ experiment result of the 9th span of Daqinghe Railway Bridge on the route from Beijing to Harbin is analyzed in this paper. Based on the lateral and vertical amplitude history gained from the experiment, the dynamic characteristics of the bridge and its response under raised-speed trains are studied. The relationship between different speed and organization of passing train and the bridge's lateral and vertical amplitude and forced vibration frequency are summarized. Also, the vibration mode of the bridge, the weakness of the structure and its reinforcing method are discussed in this paper.