Abstract: A dynamic analysis model is established for a train-bridge system subjected to a collision-load. The time history curve of a floating-ice collision load is obtained by the site experiment at the Songhua River Bridge, and it is taken as an excitation load on the bridge piers. A computer code is programed. By taking a 5×32 m simply-supported single-track high-speed railway bridge with PC box girders as a case study, the dynamic responses of railway bridges subjected to a floating-ice collision and their influences on the running safety of high-speed trains are analyzed. The whole time periods of a high-speed train running on the bridge are simulated under two conditions with and without floating ice-sheet striking on the bridge piers, from which the dynamic responses such as displacements and accelerations of the bridge, and the running safety indices such as derailment factors and offload factors of the train vehicles are investigated. The results show that the collision of floating ice has an obvious effect on the dynamic responses of the bridge and the train vehicle. The collision action obviously increases the dynamic responses of the bridge and the running vehicles. When the peak of the ice collision load reaches to 4000 kN, the offload factor of a running vehicle has exceeded 0.6, the allowance value in the Chinese code. The collision load should be treated as an important force considered in the dynamic design of high-speed railway bridges.