<p>This paper develops a new solution for evaluating the stability of finite slopes subjected to rainfall using the limit equilibrium method. Specifically, the study incorporates the size effect of slopes (i.e., the slope length) into the analysis of rainfall infiltration and its impact on the slope stability. The soil above the wetting front is categorized into a saturated zone and a transitional zone based on the volumetric water content. A new model is then proposed to calculate the expansion rate of the wetting front, accounting for the seepage force within the saturated zone. Both the interface between the saturated and transitional zones and the wetting front are considered as potential failure surfaces, and slope stability is subsequently assessed using the limit equilibrium approach. The proposed method is validated through three case studies involving both rainfall infiltration modeling and slope stability analysis. The results indicate that slope length has a significant influence on the expansion rate of the wetting front. However, the safety factor of the slope is found to be independent of slope length. Overall, the proposed method enhances the understanding of slope failure mechanisms and offers a novel perspective for evaluating slope stability under rainfall conditions.</p>