Abstract: The influence of spatial variation of seismic ground motion on the dynamic response of a train-bridge system is studied. In term of the site characteristics, non-stationary acceleration time histories of multiple supports are generated by using an unconditional simulation algorithm based on the spectral representation. The high-passing filter in the form of a critically damped oscillator is used to obtain the consistent earthquake record including all factors of spatial variation. Then, the governing equations of motion of the train-bridge system during earthquakes are established in a absolute coordinate system, in which displacement time histories of a seismic excitation are exerted on the bridge supports. Finally, a high-speed train with eight vehicles running over a 3-span steel truss-arch bridge subjected to earthquakes is taken as a case study in the consideration of the wave passage effect and full spatial variation. Numerical results show that the full spatial variation of seismic ground motion should be considered in order to obtain the safe response of a train subsystem at all train speeds.