Abstract: To ensure the security of the train running on the track during an earthquake, based on the method of ABAQUS software and FORTRAN language, a three-dimensional numerical analysis model was established for ballast-less track-subgrade-foundation of high-speed railway in this paper, the dynamic response law of elastic homogeneous subgrade caused by seismic-train moving load was analyzed. The Imperial Valley seismic wave was input bidirectionally from the bottom of the model, and the FORTRAN subroutine was compiled to implement the train moving load. In the condition of ignoring the influence of track irregularity and wheel-rail relationship, numerical calculations were implemented including the dynamic displacement, acceleration, and frequency spectrum of the subgrade at different train speeds under the combined action of the seismic and moving load, which shows that when the seismic and train moving load acts together, the vertical positive displacement of the subgrade is significantly affected by the seismic load. Its acceleration and frequency spectrum are more prominently affected by the moving load, and the critical speed of the subgrade under the combined dual load is 70 m/s (252 km/h).