Abstract: To investigate the influence of surface surcharge on the structural mechanical response and failure mechanism of shield tunnels in soft clay strata, a 1∶5 physical model test was conducted to simulate the mechanical behaviors of stratum resistance, segments, bolts, and reinforcement in detail. A three-ring full-scale finite element model was established using ABAQUS to systematically analyze the structural response characteristics under different surcharge loading positions and burial depths. The results show that the tunnel convergence deformation exhibits a five-stage evolution process with increasing load, i.e., elasticity, deformation development, rapid instability, bearing capacity degredation, and failure. The formation of plastic hinges due to yielding of longitudinal joint bolts is critical to the overall failure of the structure. Under the ultimate state, the successive formation of four plastic hinges leads to the instability of the three-times statically indeterminate system, and the structure ultimately exhibits a "horizontal duck-egg" failure mode characterized by vertical compression and horizontal expansion, with vertical convergence deformation reaching 22.56% of the tunnel diameter. When the burial depth increases from 6.6 m to 19.8 m, the convergence deformation under the same surcharge load decreases by approximately 67%, and the maximum bending moment decreases by 49%. An increase in the eccentricity of the surface surcharge induces a redistribution of internal forces, shifting the locations of the maximum bending moments from the crown to the haunches. When the eccentricity exceeds 0.75 D, the deformations can be controlled within the allowable warning limits specified by the standards.