By the excitation load function corresponding to the irregularity management standard the vertical load of the train is simulated. Based on the finite difference software FLAC3D the three-dimensional dynamic coupling finite difference model of track-embankment-pile-soil composite foundation is established. Focuses on the analysis of the dynamic response characteristics of the embankment, pile and soil foundation caused by the change of foundation, pile and cushion elastic modulus and cushion thickness. Results show: by the excitation load, the centre pile dynamic stresses are maximum, piles dynamic stress away from the centre side pile decreases gradually. The dynamic response of the pile and soil caused by subgrade surface elastic modulus variation has a little effect with more obvious by the cushion effect. With the increase of elastic modulus and thickness of cushion, the dynamic interaction between pile and cushion is increased while the dynamic interaction between soil and cushion is weakened. Therefore, the bearing capacity of the pile is fully utilized. With the increase of the elastic modulus of the pile, the dynamic stress of pile top increases correspondingly, but the dynamic stress increases gradually, and the pile bears most of the load, thus effectively reduce the dynamic load of the foundation soil.