To investigate the ultimate bearing capacity of shield tunnel segments during service, a full-scale experimental investigation was conducted. Using three rings of service-aged segments as test subjects, the experimental testing content and loading scheme were formulated. The segments underwent three-stage loading to simulate static loading tests under overburden pressure, with monitoring of overall convergence deformation, joint misalignment, longitudinal joint opening, and segment cracks during the loading process. The stress distribution, failure modes, and ultimate bearing capacity of the middle ring segments were analyzed. The results indicate that under a simulated burial depth of 15 m, the overall structural deformation of the segments was minimal. The deformation of the segments was divided into three stages, with rapid increases in overall convergence deformation when the relative displacement between the crown and invert exceeded 2.83‰D. The failure cracks in the segments were primarily concentrated around the bolt holes and longitudinal joint edges.