Abstract: The excavation area of the transition section of combined and separate construction in the Shiziyuan Tunnel is 345 m2, and this transition section passes through Wangjiaping No.1 fault with high geostress. In order to solve construction problems faced by super-large section tunnel crossing the fault zone with high geostress, such as primary support deformation and secondary lining cracking, a combination of numerical simulation and engineering analogy is used based on geological conditions to compare and select the tunnel section form, determine structural support parameters, and propose a new construction method. Practice shows that this construction method can solve problems such as difficulty in tunnel construction and difficulty in controlling deformation.