In light of the rapid expansion of underground rail transit systems and the growing requirements for tunnel operation and maintenance, the longitudinal structural resilience of shield tunnels has emerged as a critical research topic in the field of engineering. In this paper, the longitudinal differential settlement is employed as a performance index, and the ratio of residual performance to normal performance of differential settlements is defined as the resilience metric Re, thus a new model using longitudinal relative differential settlement as the index of tunnel structural resilience performance is proposed. Based on a case study in which a newly constructed shield tunnel of Shanghai suburban railway airport link line undercrosses the existing Metro Line 15 tunnel, the variations in tunnel deformation with respect to tunneling distance and construction schedule are analyzed. Then, the degradation characteristics of structural performance during both the disturbance stage and the recovery stage are effectively captured. Finally, the proposed model is applied to evaluate the structural resilience of existing metro tunnels. The results show that 32.3% of the performance loss is attributed to the new tunnel undercrossing during the first 38 days. After the completion of the grouting reinforcement, the tunnel performance is improved from 0.677 to 0.868; this improvement accounts for approximately 59.1% of the performance loss during the crossing period. Eventually, the resilience metric Re is calculated as 0.764, indicating a high level of resilience for the existing metro tunnel in this case. Moreover, other performance indices related to the longitudinal settlement of the tunnel are compared to validate the rationality and applicability of the proposed performance index.