Abstract: To study the slope stability of pumped storage power stations under complicated conditions, the overburden slope on the right bank of the lower reservoir dam of the Qiannan Pumped Storage Power Station was taken as the research object. According to on-site conditions, the slope was divided into six working conditions. The mechanical parameters of the overburden were fitted based on condition 6, yielding cohesion values of 20 kPa and 17 kPa under natural and saturated conditions, respectively. Using the fitted mechanical parameters, numerical calculation and analysis of slope stability for working conditions 1 to 5 were conducted with the SLOPE/W module in Geo-Studio. The results showed that the safety factors of the original slope were 1.548 under natural conditions and 1.319 under rainstorm conditions, both indicating a stable state. After excavation at slope ratios of 1 ∶1 and 1 ∶0.6, the safety factors were 1.172 and 1.143 under natural conditions, respectively, representing basically stable to stable states. Under rainstorm conditions, the safety factor dropped to 1.018, suggesting local instability. The calculated results were consistent with the actual slope conditions on site, verifying the scientificity and rationality of the fitted parameters. Accordingly, targeted treatment measures were proposed, and the calculation results demonstrated that the slope condition could meet the design specification requirements under all working conditions after treatment. The research results can provide a reference for similar slope projects.