Groundwater played a significant role in the stability of reservoir slopes. A landslide in reservoir area was taken as an example through analyzing its deformation characteristics and professional monitoring data. By the regulated scheme of Three Gorges Reservoir and rainfall conditions, based on theories of unsaturated seepage and limit equilibrium, eight working conditions were set for seepage and stability analysis of the landslide. Under conditions of water level fluctuation from 175 meters to 145 meters and rainfall, the analysis adopted Geo-Studio software based on finite element method. Results show that the reservoir water level changes exactly in accordance with the groundwater level, and rainfall has some effect on water level of the landslide’s back. Slope safety factor decreases with the rise of water level or the increase of rising rate. Moreover, slope safety factor firstly decreases and then increases with the drop of water level. Finally, slope safety factor decreases a little under the conditions of rainfall.