The coupling of water level fluctuations and heavy rainfall in the Three Gorges reservoir area poses a significant threat to the stability of bank slopes, especially in landslide areas with complex geological conditions. In this study, the Huasushu slope in Fengjie County, Chongqing, was taken as the research object and, based on a field investigation and monitoring data, two- and three-dimensional numerical models were constructed to analyze the response mechanism of the slope under the combined effects of different reservoir water level decreases and rainfall. In addition, the safety coefficients under each working condition were calculated using the Morgenstern–Price method. The results show that it is difficult to trigger significant deformation with a single water level drop or rainfall. However, when the reservoir water level drops more than 10 m within a short period of time and is superimposed with strong rainfall, the landslide body is prone to plastic zone extension and significant displacement, showing typical strain localization characteristics. The three-dimensional model further reveals the spatial distribution characteristics of the landslide deformation area, which helps to accurately identify potential destabilization locations. The research results provide theoretical support for the construction of early warning systems for reservoir bank slopes and have reference value for the development of disaster mitigation engineering measures based on the coupling mechanism of rainwater and reservoir water.

Slope failure generally starts from a single point, where a local failure surface forms, and then progresses to the overall failure. Based on this behavior, this paper proposes a multi‐criterion stability evaluation approach for describing progressive failure process of slope. The criteria for slope body failure (main thrust, surplus friction resistance, comprehensive displacement, and surplus displacement) are adopted to evaluate the stability during progressive failure process. The sliding surface boundary method (SBM), partial strength reduction method (PSRM), and free surface boundary conditions for slope stability numerical analysis are adopted, in which the gradual movement of the critical stress state of the sliding surface is simulated for selected boundary conditions, reproducing the entire process of gradual slope failure. The case study of the Dianzhan slope located in the Wufeng County in Hubei Province shows that the multi‐criterion stability evaluation approach adopting PSRM and SBM can better describe the evolution of various slope stability and failure characteristics. Comparing the stability coefficients calculated by traditional methods with the method proposed herein provides a novel theoretical basis of slope stability assessment, early instability warning, and slip‐resistant design.