Abstract: The conventional stability design method for the composite ground improved with rigid piles (CGIRP) to support embankment assumes a simultaneous shear failure of the piles with the failure slip. Based on the previous studies, a finite difference method is adopted to analyze the stability of CGIRP by considering different simulation methods for post-failure behaviors and failure orders of piles. The analysis reveals that unreinforced rigid piles in the composite foundation firstly have brittle bending failure in local regions. The stress relief due to failure of pile leads to a significant increase of bending moment in the neighboring piles, causing the progressive bending failure of the neighboring piles. The progressive failure of piles finally triggers the catastrophic collapse of the CGIRP-supported embankment. The stability of CGIRP-supported embankments will be overestimated remarkably when assuming a simultaneous failure of the piles with the failure slip. The progressive failure caused by local failure of piles should be considered in practical design. Base on the progressive failure control method, the concept of key piles and the non-uniform strength design method are proposed. The stability of CGIRP can be improved efficiently and remarkably by increasing the strength and ductility of the key piles.