Abstract: Near-fault long-period pulsed ground motion may cause serious damage to submarine shield tunnel structure./t/nThe longitudinal seismic response analysis of cross-strait shield tunnels has challenges such as large spatial dimensions, dense assembly of pipe segments and bolt arrangements, and strong nonlinear soil-structure interaction. These factors significantly reduce the computational feasibility of refined longitudinal tunnel models. In view of this, a dynamic substructure method for seismic response analysis of the 2.7 km-long Suai submarine shield tunnel was developed based on the response displacement method. Near-fault pulse and far-field ground motions were selected to investigate the differences in longitudinal seismic responses of the shield tunnel, and an optimal parameter was proposed to characterize the tunnel’s longitudinal damage potential. The results indicate that, compared to far-field ground motions, the velocity pulse effect inherent in near-fault ground motions induces more intense seismic responses in the submarine shield tunnel. The longitudinal seismic response of the structure is more sensitive to low-frequency seismic waves, and the spatial distribution pattern of seismic stress is significantly altered. Under near-fault conditions, peak seismic stress is concentrated at the tunnel shoulder, whereas under far-field excitation, it occurs at the tunnel foot. For evaluating the longitudinal seismic response of submarine shield tunnels, the root-mean-square velocity (RMSV) is recommended as the optimal parameter to characterize structural damage potential.