Abstract: Variation in reservoir water level is the main factor inducing the deformation and instability of bank slopes. In order to explore the groundwater dynamic effect of the slope formed by the collapse of toppling deformed rock mass under the change in reservoir water level, the Zhaoziping landslide near the Miaowei Hydropower Station on the Lancangjiang River in Yunnan was taken as the research object, and the landslide morphology and structure characteristics were determined by field geological survey and exploration. The deformation and instability mechanism of the landslide under the action of groundwater dynamic was analyzed in detail using the deformation monitoring data. They are validated based on the unsaturated soil mechanics theory and finite element method. The results show that the Zhaoziping bank slope is an accumulation slope formed by the sliding of the upper strongly toppled rock mass along the fracture surface after the deformation and failure of the original toppled rock mass. The stratified accumulation of schistose rock in the slope indicates that it retains some structural characteristics of toppled rock mass. After the reservoir impoundment, because the loose toppling accumulation body creates good conditions for reservoir water to infiltrate into the slope, the groundwater level rises rapidly with the reservoir water level rising, which leads to the increase in pore water pressure and the decrease in effective stress in the landslide resistance section, thus the stability of the landslide decreases, and the landslide is liable to slide along the bedrock cover interface evolved from the fracture surface.