Currently, the slope stability analysis under the combined effects of reservoir water level and rainfall is estimated commonly via the deterministic analysis methods. However, these methods cannot accurately evaluate the slope stability due to the inherent spatial variability of geotechnical parameters. Therefore, in this study, the slope stability influenced by reservoir water level and rainfall is analyzed based on the monitored data during an annual cycle of rainfall and reservoir water level, taking the bank slope of Heishui River in Baihetan reservoir area as an example. Firstly, three most unfavorable cases are determined through deterministic analysis. Accordingly, the influences of stationary and non-stationary random fields on the results of slope reliability analysis are compared using the stochastic finite difference method (RFDM), considering the spatial variability of effective cohesion c′、effective friction angle φ′ and saturated permeability coefficient ks, respectively. Results show that, compared with the rainfall infiltration, the reservoir water level fluctuation plays a crucial role in slope stability, and the minimum safety factor occurs during the rapid drawdown. Meanwhile, the combined effects of rainfall and reservoir water level will significantly increase the slope failure probability and sliding volume. In addition, the depth-dependent characteristics of geotechnical parameters require to be considered when conducting stochastic analyses of slope stability, otherwise the slope stability will be underestimated.