Abstract: Aiming at the complex problem of quantitative evaluation of the landslide stability under the condition of reservoir water level change, the authors in this paper considered the influence mechanism of rainfall and reservoir water level changes on groundwater seepage field, and adopted the basic theory of saturated-unsaturated seepage and seepage simulation finite element method to simulate the Yangjiaotan landside stability in the reservoir area under 6 different conditions. The results show that: ① Rainfall has an impact on the groundwater seepage field, with the greatest impact in the middle of the groundwater level and little impact on the front and back. Under rainfall conditions, the stability of the landslide decreases with the increase in rainfall duration. The landslide began to slip after reaching a certain stage, and the landslide stability coefficient keep unchanged. ② Under the condition of the reservoir water level, the front edge of the landslide was mainly affected, and groundwater level changes rapidly with the change of the reservoir water level. The landslide stability coefficient shows a trend of first decreasing and then increasing with the rising reservoir water level. ③ The sudden rise of the groundwater level has limited impact on the floating effect, but it has a greater impact on counter poising. Besides, it also reduces the impact of the seepage force, which has a positive effect on the stability of the landslide. The sudden drop of the groundwater level increases the seepage force, weakening the effect of leading-edge reservoir water level on counter posing, so the possibility of landslide instability is greatest. The research results can provide a scientific basis for the prediction of the current stability and development trend of such landslides in the reservoir area.