The Daowu Mountain tunnel under construction is a 3-lane super-long first grade highway tunnel. The excavation span in shallow section of grade V surrounding rock at the portal of the tunnel is 16.85 m,and the excavation area is 163.55 m2.The original design construction method is both side heading method and three-step seven-part method is adopted after design changes.Through three-dimensional numerical simulation analysis,the vault settlement,clearance convergence and the initial support stress during construction is analyzed.According to the analysis results,judge the stability of surrounding rock,initial support safety.The numerical results show that the three-step seven-part construction method is safe in shallow portal part of grade V surrounding rock for the 3-lane tunnel.The results could provide basis and reference for similar design and construction.