To study the characteristics of mechanical behavior of the multi-arch tunnel in the process of two-way single-hole excavation, the Leijiatai multi-arch tunnel of Anxiang-Cili Expressway in Hunan Province is taken as the engineering background. A three-dimensional numerical model is established by using the finite element software Midas GTS/NX. The stress and strain of the middle partition wall, surrounding rock pressure, and surrounding rock displacement are analyzed by comparing the actual two-way single-hole excavation process with the traditional one-way double-hole excavation process. The results show that the construction period of two-way single-hole excavation is about 2/3 times that of normal excavation. The two-way single-hole excavation scheme and the normal excavation scheme do not produce largely different surrounding rock pressure and surrounding rock displacement in values. After the construction, the stress of the middle partition wall in the two schemes is almost the same. However, during the construction process, the two-way single-hole excavation causes torque force in the middle partition wall. Thus, corresponding effective support should be made for the torsion resistance in the two-way single-hole excavation scheme. In the two-way single-hole excavation, both ends of the middle partition wall have lateral offset to the excavated section, which should be considered in the design optimization of middle partition wall in the future.