A two-and-a-half-dimension finite element method (2.5D FEM) was established to investigate the surface vibration of the unsaturated ground subjected to moving loads caused by high-speed trains. The track structure was simplified as an Euler beam resting on an unsaturated porous half-space. The Galerkin method was used and the governor equations of unsaturated soil of 2.5D in frequency-wavenumber domain was derived by applying the Fourier transform with respect to time and the load moving direction. The influences of train speed and water saturation of unsaturated ground on ground vibration and excess pore water pressure are analyzed. Results show that, at the track center, the displacement amplitude largely decreases when the water saturation decreases from 100% (fully saturated) to 99% (nearly saturated); for a given speed, the ground vibration displacement of unsaturated ground attenuates faster with time than the saturated ground. At 8 m away from the track center, the displacement amplitude of the unsaturated ground is larger than that of the saturated ground when the train speed is below 250 km?h-1; as the speed increasing, the duration time of the unsaturated ground vibration displacement becomes shorter as the speed increases, while of the saturated ground it becomes longer. The displacement amplitude at 200 km?h-1 is larger than the other speed near the track (less than 5m) and attenuates rapidly at an equal rate. The rebound phenomenon of acceleration may occur at some train speed, and the location is strongly related to the train speed. The excess pore water pressure is mainly distributes within 4.5 m below the ground surface and the maximum amplitude is located at 1.5~2.0 m depth and decreases significantly as the water saturation decreases.