Abstract: Soft soil subgrade is commonly reinforced with rigid piles now in order to control the stability of the embankment. The broken mechansim of piles is introduced to analyse the instability and failure mode of soft soil subgrade reinforced with rigid piles using the finit element software ABAQUS.Compared to the traditional numerical simulation method, this theory shows that progressive failure occurs among rigid piles subjected to embankment loading. On this basis, considering the likely occurrence of bending failure, the critical ratio n is proposed as the critical value for judging shearing failure or bending failure of pile. It occurs preferentially also as termination criterion for the broken mechansim of piles. The large errors of quantitative calculation using numerical simulation software can be avoided reasonably. Finally, the proposed numerical simulation is compared with the traditional numerical simulation and the numerical simulation of equivalent sand pile method. The results reflect the rationality and reliability of the proposed method. In engineering, the stability of embankment can be improved by limiting the horizontal displacement or increasing the bending strength of the front piles.