Based on the phenomenon of stress concentration induced by the soil arching effect and the variability of loads and soil parameters, a model for reliability analysis of stability evaluation of the pile-supported embankment was built, and the reliability index calculation method and flow chart were presented in this paper. Taking a typical pile-supported embankment of a highway as an example for stability analysis, the reinforced pile length for the embankment was designed with the safety factor method and reliability index method, respectively, and sensitivity analysis of the reliability index was conducted based on the variability of loads and soil parameters. The results show that the variability of loads and soil parameters has a large influence on the stability of the pile-supported embankment, and it is more reliable and reasonable to use the reliability index method to design the reinforced pile length. The results also indicate that the limit lateral resistance of the second-layer soil and the variability of additional loads on the embankment surface should be given close attention, and the internal friction angle of embankment filling and the ultimate resistance of the reinforced pile can be treated as constants.