Abstract: In order to improve the overall stability of the composite foundation of high fill embankment, this paper studies the composite foundation under flexible load, aiming to construct an overall stability model considering the soil arching effect at the top of the pile and the flow around the pile, which provides a theoretical basis for engineering design. Based on the failure mode of the arc sliding surface, the overall stability model of the composite foundation under the flexible load of the high fill embankment was established, and the calculation formula of the stability coefficient of the flow around the piles of the composite foundation was derived, and the rationality of the formula was verified by the laboratory model test and numerical simulation. The overall stability model of the composite foundation considering the soil arch at the top of the pile and the flow circulation effect between the piles was successfully established, and the calculation formula of the stability coefficient of the flow around the piles was obtained. Experimental and numerical simulation results show that the formula has high rationality. Further analysis shows that the stability coefficient of the flow around the piles increases with the increase of cohesion, but decreases with the increase of the height of the fill embankment and the spacing between the piles. The results of parameter sensitivity analysis showed that the influencing relationship was as follows: internal friction angle> pile spacing> height of fill embankment > cohesion. The research results provide an important theoretical basis for the design and stability evaluation of high-fill embankment composite foundation.