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Abstract A new track-multilayer ground model was established to investigate railway subgrade dynamic responses induced by moving train load in this paper. The ground structure was modeled by an elastic layer overlying an unsaturated porous elastic half space. The dynamic governing equations of the three-phase porous medium, which are easy to be degraded to Biot's theory, were derived with consideration of both viscous drag and inertial coupling between pore fluids and soil skeleton as well as capillary pressure. The model solutions were obtained based on dynamic stiffness matrix method and Fourier transform and introducing corresponding boundary condition. The vertical displacement on the subgrade top surface and the pore water pressure along the depth were studied. The numerical results show that the effects of saturation, vehicle speed, train axle load and subgrade bed material properties on the subgrade responses are significant. Highlights • A coupling track-elastic subgrade bed-unsaturated subgrade model is proposed. • Dynamic response of the unsaturated subgrade caused by moving train load is studied. • The effects of saturation, vehicle speed and train axle load are significant. • Subgrade bed thickness and modulus should be strictly controlled in design of ground. [ABSTRACT FROM AUTHOR]