Abstract: Reservoir water level fluctuations significantly affect stability of bank slopes, among which rapid drawdown is a critical factor introducing slope instability and poses a major threat to reservoir safety. To investigate the dynamic influence of drawdown rate on slope stability, this study takes the Zhangjiawan slope at the Tingzikou Hydraulic Project as a case study. Based on geological surveys and GNSS monitoring data, the spatiotemporal correlation between slope deformation and reservoir water level changes was analyzed. Numerical simulations were performed using GeoStudio to examine the seepage response and stability evolution of the slope under various drawdown rates. The results show that: ① A higher drawdown rate leads to a more pronounced reduction in slope stability. When the water level dropped at a rate of 1 m/d, the factor of safety (FoS) sharply decreased from 1.40 to 1.01 within 12 days; in contrast, at a drawdown rate of 0.5 m/d, the FoS only decreased to 1.11, with a notably slower decline. ② Drastic changes in pressure head and hydraulic gradient within the seepage field are the primary mechanisms underlying stability deterioration. During rapid drawdown, the pressure head at the slope toe decreased rapidly from 287.28 kPa to 95.76 kPa, and the seepage lag significantly weakened the shear strength of the sliding zone. ③ The numerical simulation results are consistent with field monitoring data: a rapid drawdown of 3.61 m in February 2022 corresponded to a slope displacement of 1.99 m, while a drawdown of 2.11 m in September 2022 resulted in a displacement of 1.16 m. The above two field observations align with the simulated trend of a sharp decline of the FoS following rapid drawdown. This study systematically elucidates the seepage-mechanical coupling mechanism through which rapid reservoir drawdown affects slope stability, providing a theoretical basis for dynamic risk assessment and engineering prevention and control of reservoir bank slopes.