Abstract: In order to explore the influence of landslide stability by the change of reservoir water level, a reservoir bank landslide in Southwest China is researched. According to the engineering geological conditions and genetic mechanism of landslide, the effect of variation of water level impacting on the landslide stability and sliding mode based on fluid-solid coupling is analyzed through a three-dimensional numerical model. The plastic zone distribution and X-displacements under nature state, initial impoundment, water level rise and water level fall are obtained through numerical calculation. The stability of reservoir bank landslide under different water levels is analyzed comprehensively. The results of numerical calculation and actual deformation features are also taken into account in the analysis. The results show the follows. The landslide deformation due to the first water storage of reservoir can cause the slope into unstable state. The water level rise has little influences on the landslide stability. The landslide stability is reduced sharply and the slope is likely to occur instability damage when the water level falls. The failure mode of landslide would be diverted from push mode to drag mode after the water storage of reservoir.