Abstract: In view of the problem that the surrounding rock is prone to instability and failure after excavation of underground chambers of large-scale hydropower stations, we built a three-dimensional numerical simulation model for underground chamber group excavation of Zhongyu Hydropower Station, considering the influence of crustal stress on the stability of surrounding rock. The main powerhouse, main transformation tunnel and tail adjustment chamber were greatly studied. Different analysis sections were selected to compare and analyze the distribution laws of displacement, stress, plastic zone and yield zone of surrounding rock after excavation of the chambers in unsupported and supported conditions. The results showed that without effective support, under the influence of self-weight of rock mass and crustal stress, the original support force could not be compensated after the excavation of the underground chambers, stress will be concentrated on the excavation area, and the deformation of surrounding rock could not be effectively controlled. After the underground chamber group was supported, the maximum principal stresses on the surrounding rock were significantly reduced, with a maximum decrease of 91.11%, preventing localized stress concentrations and destabilization. The maximum reduction in displacement was 23.08%, and the maximum reduction in the depth of the plastic zones and yield zones was 31.91%, effectively controlling the unfavorable deformation of the surrounding rock, preventing the expansion of the plastic zones and yield zones of the rock mass around the tunnel, and ensuring the safe and efficient construction of the underground chamber group.