Under the condition of large-span variable section, tunnel excavation is easy to cause large structural deformation. the deformation and stress change of tunnel construction under different variable sections are summarized, the disaster-causing mechanism of tunnel are analyzed. The variable section significantly increases the deformation of the nearby rock at the vault and side wall, and the stress change of the rock at the arch foot is obvious. Compared with the radial deformation, the vertical deformation of tunnel on the continuous variable section excavation is larger. When the small section turns to the large section, the deformation is larger than the large section, and the research results can provide a reference for the design and construction of similar tunnel group.