Abstract: To address the poor self-stabilization capacity of surrounding rock and the frequent failure of single-layer primary support in shallow-buried large-span loess tunnels, this study establishes numerical models of tunnel excavation for the Baishi No. 2 Tunnel in Lanzhou, Gansu Province, under two conditions of conventional single-layer and novel double-layer primary supports. The evolution of surrounding rock convergence and support stress under different support conditions was systematically analyzed to investigate the mechanical and deformation characteristics of the double-layer primary support system. Numerical results were further validated through comparison with field monitoring data. The results indicate that, compared with the single-layer system, the double-layer support effectively mobilizes the self-bearing capacity of the surrounding rock by hierarchically distributing ground pressure, thereby reducing inner support stress by about 80%. Under the double-layer condition, the maximum settlement of the surrounding rock reached 65.2 mm, slightly higher than the 58.8 mm observed for the single-layer support. However, the double-layer structure better accommodated the initial deformation, released deformation energy, and improved the long-term stability of the support system. The convergence deformation of the surrounding rock and the contact pressure on the primary support exhibited a three-stage evolution: rapid growth, slow growth, and final stabilization. The installation of the inner primary support effectively reduced the growth rates of deformation and contact pressure. These findings confirm that the double-layer primary support system offers excellent engineering applicability for shallow-buried large-span loess tunnels.