Abstract: To address the face stability issue of shield tunnels constructed in highly permeable sandy soils, a calculation method for the ultimate support pressure at the tunnel face is developed based on the upper bound theorem of limit analysis. A three-dimensional rotational failure mechanism is constructed using a spatial discretization technique. By comparing the proposed method with existing analytical solutions and further validating it through numerical modeling, a sensitivity analysis of key parameters is conducted. The results indicate that: (1) the discrepancy between the proposed method and the existing analytical solutions is within 7%, while achieving significantly higher computational efficiency; (2) although the difference from numerical simulation results is approximately 20%, the proposed method provides a reference for effectively controlling seepage at the tunnel face; (3) groundwater level exerts the most pronounced influence on the ultimate support pressure, followed by internal friction angle, while soil unit weight has the least effect. A case study from an actual metro shield tunnel project further verifies the reliability of the proposed calculation method.