Abstract: The water level change triggered by reservoir operation will produce significant disturbance effect on the slope of the reservoir bank, and the slope instability caused by the disturbance effect of this dynamic water action has become the core problem threatening the safety of the reservoir, therefore, the study of the impact of the reservoir water level change on the stability of the slope of the reservoir bank is of far-reaching significance.① In this paper, the Zhangjiawan slope of Tingzikou Water Conservancy Hub is taken as the research object, and a systematic study is carried out around the influence of reservoir water level change on slope stability. The temporal and spatial relationship between slope deformation and water level change is revealed through geological condition analysis and GNSS monitoring data, and Geo-Studio software is used to simulate the response process of slopes with different water level decline rates, and the dynamic evolution law of slope stability is explored after the water level is changed with different decline rates. The results of the study show that: (1) The greater the rate of water level decline, the more significant the impact on slope stability. Through comprehensive analysis using multiple methods, a quantitative relationship between the rate of rapid water level decline and slope stability is established. When the water level declines at a rate of 1 m/day, the safety factor of the slope sharply decreases from 1.40 to 1.01 within 12 days. In contrast, at a water level decline rate of 0.5 m/day, the safety factor decreases to 1.11 within the same water level range, demonstrating a significantly slower rate of decrease. (2) The drastic changes in the pressure head and hydraulic gradient of the seepage field are identified as the primary driving mechanisms for the reduction in slope stability. The delayed effects of seepage induce a decrease in shear strength along the sliding zone, with the pressure head at the foot of the slope rapidly dropping from a maximum of 287.28 kPa at the highest water level to a minimum of 95.76 kPa at the lowest water level. (3) The consistency among reservoir water level fluctuations, GNSS-monitored embankment slope displacements, and numerical simulation results was systematically validated through integrated data analysis. A 3.61 m water level drop in February 2022 was followed by a slope displacement of approximately 1.99 m, as indicated by GNSS monitoring data. In September 2022, after a 2.11 m water level drop, the slope displacement reached 1.16 m. These results closely match the trends predicted by the numerical model, where the safety factor rapidly decreases following a rapid drop in water levels. This paper reveals the complex influence law of sudden drop of reservoir water level on the stability of reservoir slopes, and provides a new perspective for the dynamic risk assessment of reservoir slopes.