In order to study the TBM excavation stability of the tunnel group with small clear distance under different surrounding rock conditions, relying on the Buji South Ring Road tunnel project, the finite element software Midas is used to establish a three-dimensional numerical model to simulate the TBM excavation process of the four pilot tunnels. By analyzing the mutual influence of TBM tunneling under different surrounding rock grades, the deformation characteristics of each stage of the tunnel pilot tunnel excavation were systematically revealed, and on-site verification is carried out for the simulation results. The research results show that:1) When a single pilot tunnel is excavated, the vault settlement and the ground surface settlement show a non-linear growth trend with the excavation footage and finally tend to a stable state, and there is a significant positive correlation between the tunnel convergence deformation and the excavation footage;2) During the excavation process of the multi-pilot tunnel group, the construction of subsequent pilot tunnels will trigger a superposition effect on the already penetrated pilot tunnels. The specific manifestations are as follows: the vault settlement, horizontal displacement and ground surface settlement show a non-linear cumulative growth, while the horizontal convergence value shows a non-linear decay characteristic. Among them, the superposition effect in the section of Grade V surrounding rock is the most significant, and the settlement reaches its peak value when the pilot tunnel is completely penetrated. Based on the research results, the construction plan was optimized. By dynamically regulating the excavation and support parameters throughout the whole process, the tunnel deformation was finally controlled within the allowable range, effectively ensuring the construction safety.