Abstract: To accurately capture its nonlinear characteristics under surcharge, an approach for the subgrade reaction of shield tunnels is implemented on the basis of the soil strength design method (MSD method) and the unified hardening model (UH model). The practical simplified version is proposed by conducting the description of the mechanical properties of the entire soil zone with constitutive curves of soils at the height of tunnel center. Furthermore, using the statistically derived UH constitutive parameters for soil layers ④ and ⑤₁ in Shanghai, the subgrade reactions for both soil layers are predicted and fitted by using the hyperbolic curve function. After the secondary fitting process is conducted to obtain the initial stiffness and the ultimate strength in relation to the parameters of the constitutive model, the functions for subgrade reactions of shield tunnels in Shanghai are established. Eventually, the multifactorial evaluation of shield tunnels in Shanghai under surcharge conditions is performed, confirming the capacity of the developed formulas for predicting the large deformation of tunnels under surcharge. The convergence deformation of the tunnels under surcharge is more sensitive to the initial stiffness of subgrade reactions, governed by various soil parameters such as κ/λ and confining pressure, than to its ultimate strength.