Abstract: To ensure the safe operation of shield tunnels, the degradation law of the waterproof performance of gaskets in shield tunnels under joint deformation was investigated using theoretical analysis and numerical simulation. A four-stage waterproof failure model for shield tunnel gaskets was established, and three evaluation indexes for characterizing waterproof performance were proposed. On this basis, the influence law of joint deformation on the waterproof performance of gaskets was analyzed via numerical simulation. The results show that the gasket interface exhibits a corrugated plate morphology under compression, with maximum contact pressures occurring at the crests and edges of the corrugations. The proposed evaluation indices can identify the waterproof failure state of the interface from three dimensions: leakage channel, interface stress level, and safety reserve, which exhibit stronger systematicity and applicability than single evaluation indices. A synergistic deterioration effect is observed under combined joint deformation, and joint opening is the dominant factor leading to the nonlinear degradation of waterproof performance. The most severe degradation of waterproof performance occurs under the coupling of joint opening with longitudinal and transverse dislocation.