Abstract: For the ultra-high concrete face rockfill dams, natural sand and gravel materials are used as the dam materials for rockfill dam projects. The combined impermeability stability of the dam partition materials is very important to the dam safety. In this study, the self-developed high-head large-scale permeability test equipments are used to conduct the combined seepage failure tests on the sand and gravel dam materials for Cihaxia Hydropower Station. The evolution process of seepage characteristics of the filling materials in each district are monitored. The anti-filtering protection effects of the transition materials on the cushion materials are verified. The results may provide data reference for the optimization of gradation design of dam filling materials of Cihaxia Hydropower Station and the demonstration of seepage stability safety.