Because reservoir water is one of the master factor inducing slope landslide in the Three Gorges area, it is significant to study the stability of landslide under the condition of water level fluctuation of reservoirs. We make a study of the stability of Huangtupo riverside slumping mass #1 in Three Gorges area under the condition of water level fluctuation of reservoirs by the measure of geologic survey and in situ monitoring and theoretical analysis as well as numerical simulation. We make a study of the relationship between reservoir water level and the landslide groundwater level in the place mentioned above based on the analysis of field monitoring data. And we also analyze the deep displacement changed over time at different altitudes of the landslide as well as the influence of the variation of water level of reservoirs on the deformation of landslide via the same data. We make a simulation of landslide mentioned above through “3DDEC” and analyze the changeable rule of stress-strain of landslide under the variation of water level of reservoirs; and we put forward the strength reduction method considering the action of drying-wetting cycle and define the method to solve the safety factor. The results show that: it is reasonable adopting “3DDEC” to anlyze sliding slope; Huangtupo riverside slumping mass #1 is in a stable state under the action of current water transfer curve; in particular, we find that the low seismic intensity has little effect on the stability of the landslide based on the analysis of the deformation of the slumping mass before and after the Badong earthquake in December 16, 2013.