The development of seepage erosion is complex and influenced by various factors. Train-induced vibrations exacerbate the complexity of the evolution of seepage erosion. The coupled CFD-DEM method was employed to study the influence of fine particle content, confining pressure, and hydraulic gradient on the seepage erosion through experimental on 8 groups of gap-graded sand samples under vibration conditions. It is found that the higher the fine particle content and confining pressure, the higher the fine particle loss ratio, axial deformation and average kinetic energy of fine particles are. The fine particle content is related to the erosion loss rate, and the smaller the fine particle content, the shorter the time to reach the erosion stability. The hydraulic gradient has relatively little influence on the axial deformation of the sample. Under vibration, the sample reaches a stable state with oscillations at a specific vibration frequency.