In order to investigate the stress and deformation characteristics of surrounding rock during the excavation of underground cavern group in pumped storage power stations, this study establishes a 3D numerical model of cavern group in weathered granite formation at the Yunfu Shuiyuanshan pumped storage power station using three-dimensional finite difference simulation software. Validated numerical simulations are conducted to analyze the full process excavation and support of the caverns, revealing the distribution and evolution patterns of displacement, stress, and plastic zones in the surrounding rock during construction. The results show that: (1) The sidewall displacements of the three caverns are larger than those of the vaults and floors. The downstream sidewall displacement of the main powerhouse is greater than that of the upstream sidewall, while floor rebound displacement surpasses the vault settlement. The main transformer cavern exhibits significantly higher upstream sidewall displacement increments than downstream counterparts due to hauler tunnel excavation. Stress and displacement contours are densely distributed between the main powerhouse and main transformer cavern. Post-excavation of hauler tunnels and tailrace surge chambers, surrounding rock stress undergoes notable changes; radial stress is released, while tangential stress increases. (2) Subsequent excavation activities induce displacement amplification, stress redistribution, and pronounced stress concentration/relaxation in pre-excavated caverns through rock mass disturbance and stress superposition. Plastic zones primarily develop between the Main Powerhouse and Main Transformer Cavern, with depths reaching 0.1–0.5 times the cavern width. To enhance global stability, pre-stressed anchor cables are recommended for reinforcement in this critical region. The results can provide references for related research.