This paper presents a full-scale model study of the mechanical behaviors of geosynthetic-reinforced pile-supported (GRPS) railway track-bed under coupled effects of changing water levels and large number of loading cycles. Four testing procedures were performed: water level increasing, loading at high water level, water level lowering and loading at low water level. The results indicate that with the water level increasing and loading at high water level, the differential settlement between the subsoil (simulated by water bag) and pile cap increased, leading to more significant soil arching effect. When enough loading cycles were applied at high water level, a stable soil arching was developed. At the stable state of soil arch, the distributions of dynamic soil stress were slightly influenced by the lowered water level and loading at low water level. In these two procedures, the overall settlement of the model varied slightly and the differential settlement stayed nearly unchanged.