Asymmetrical multi-arch tunnel is a special kind of tunnel, which has complicated mechanical characteristics of geometric asymmetry and structural asymmetry. In the asymmetrical multi-arch tunnel construction, it is inevitable to pass through the bias terrain, and the bias has great impact on the stress state of the tunnel. The finite element method is used to make numerical simulation analysis on the asymmetrical multi arch tunnel under bias terrain condition. According to the forced deformation characteristics of surrounding rocks and lining structures of the tunnels with large and small diameters in the left or right, it is concluded that the small one of the asymmetric twin-arch tunnel should be designed at the deeply-lying side in the biased state, which provides a theoretical basis for the design of the tunnel.