Abstract: Replacing the precast piles with the thin-wall cast-in-situ tubular piles to form GRPS (geosynthetic reinforced pile-supported embankment) is a new attempt in engineering application. Based on a specific engineering case, the 3-D finite element model for GRPS with capping plate and pile-net composite foundation without capping plate is analyzed. The analysis of the results shows that the capping plate can provide the stage for the embankment to form the compacted shell, which makes the soil arching play a greater role, and efficiently control the subgrade settlement and lateral deformation etc. At the moment, the geogrid tension is small because of the presence of pile cap, so the geogrid whose tensile strength will be displayed in the great degree under the low stressed conditions can be employed in the design. On the other side, as a result of asymmetric triangle of pile arrangement, the soil arching coefficient curve of pile-soil along the across section of earth bank become wave-shaped, and the geogrids are in non-uniform stress at both sides of the capping plate. The working mechanisms of GRPS are revealed from the results, which may provide the theoretical basis for engineering application.