In the super deep soft rock tunnel, the crustal stress is usually high, and the surrounding rock is weak and broken. Large deformation will inevitably occur during the construction process, resulting in the failure of the support structure. Using the stress release technology of advanced pilot tunnel to release crustal stress in advance can improve the stress state of the support structure, reduce the tunnel deformation, and ensure the safety of the support structure. This article relies on the Haba Snow Mountain Large Deformation Tunnel on the Lixiang Line, and uses methods such as literature research, numerical simulation, and on-site monitoring to study the reasonable section size of the advanced middle pilot tunnel in super deep soft rock tunnels. It analyzes the stress release effect under different section sizes of the middle pilot tunnel, and ultimately determines the reasonable section size of the middle pilot tunnel. The research results indicate that the stress release effect is ideal when the cross-sectional area of the leading middle tunnel is 0.6 times that of the main tunnel. Compared with direct excavation of the main tunnel, when using a reasonable advanced middle pilot tunnel section, the settlement of the main tunnel arch crown and the horizontal convergence values of the upper and lower steps decrease by 28.2%, 27.64%, and 26.71%, respectively, and the peak tangential stress in the surrounding rock shifts about 4 meters to the deep part of the surrounding rock. Meanwhile, the peak stress value has decreased by approximately 5.04%. The research results can provide reference and inspiration for similar large deformation tunnel projects.