Abstract: The longitudinal response deformation method suggested by the "Code for Seismic Design of Urban Rail Transit Structures" is a kind of pseudo-static method, which can be introduced to seismic response analysis of tunnel structures. It builds a beam-foundation spring model, taking dynamic free-field displacement time-history as the equivalent input. This paper put forward a way of determining the critical moment when longitudinal maximal deformation and internal force of a tunnel structure occur. The standard method was adopted to obtain the longitudinal seismic responses of a certain shield tunnel construction under SH wave oblique incidence, with the dynamic time-history method being an accurate reference. Critical moments were then applied to simplify the computational procedure from all time steps to a single step during the seismic wave duration. Although the structural displacements and bending moments calculated by the standard were close to those obtained by the dynamic time-history method, it may bring large errors of structural axial and shear forces caused by the discrete foundation springs. The application of critical moments could increase the computational efficiency, simultaneously reducing the calculation error of structural internal forces, especially that of the shear forces.