Abstract: The problem of water inrush in water-rich tunnels has become the primary problem to be solved in tunnel construction, especially in tunnels with particularly large water inflow and high water flow velocity. At present, most of the existing researches focus on the grouting reinforcement circle, which is mainly based on drainage and post-grouting. This method is feasible for surrounding rock with small water inflow and low permeability, but where it is high in water pressure and rich in groundwater, tunnels have poor performance and high cost. In view of this problem, this paper proposes a technical solution for curtain wall water blocking. Firstly, the relationship between the penetrating force and the viscosity coefficient of the slurry is analyzed. The critical flow velocity of the groundwater under the penetrating force of the grouting slurry in the porous medium is calculated, and the optimal spacing of the curtain wall from the tunnel is determined to be 2 m. Twenty-four different sizes of grouting solutions are proposed. Secondly, numerical simulation method is used to calculate the water blocking or limiting effect of the twenty-four grouting schemes. Finally, in the twenty-four models built, the scheme with a grouting depth of 30.6 m and a grouting length of 20 m is the best water shutoff scheme and is applied to the project. In the engineering application, the water in the cave is reduced by 80%, and the water blocking effect of the scheme is obvious, which can ensure the next construction of the tunnel. The research results show that the critical flow rate analysis method can economically and quickly determine the water blocking or limited discharge scheme to meet the requirements of in situ construction and grouting and water blocking. The research results can provide theoretical basis for similar engineering design.