Abstract: A dynamic model for a vehicle system, ballastless track and subgrade subjected to a moving train load is developed. By means of Fourier transform, the dynamic fundamental equations for an elastic half space are solved. The vertical displacement of the subgrade is obtained by using the contact condition between the track and a half space. The dynamic displacement of subgrade in time domain is obtained by using the Inverse Fast Fourier Transform. Through numerical examples, the variation characteristics of dynamic response of the subgrade are studied by introducing the different train speed, track stiffness and other parameters. It is shown that the amplitude of dynamic response increases with the increasing train speed, and decreases gradually with the increasing distance away from the track center along the longitudinal and vertical directions. It is also found that the rail stiffness has the most influence on the foundation dynamic response, the orbital plate stiffness takes the second place and base stiffness is in the last place. And the bend stiffness coefficient of the base is more important than other parameters in the analysis of the foundation dynamic response.