The internal force of Laoyingzui tunnel along Funing-Guangnan Highway in Yunnan Province is analyzed using the finite element method. The reasonable tunnel inner outline is obtained through adjusting the connecting method between invert pattern and curved wall.The model is developed based on structure and rock type; and the wall rock resistance is considered. The internal force of original design model and optimized model are compared and analyzed. The results provide a theoretical reference for section design of large-span tunnel.