Abstract: In view of the fundamental theory of integral response displacement method employed in lateral seismic analysis of underground structure, a kind of method that can be adopted to analyze the longitudinal seismic response of a tunnel structure is put forward. Based on the seismic response of the free field, a way to determine critical moments when longitudinal maximal deformation and internal force of a tunnel structure occurred is proposed as well. When employing this method, a static free-field analysis model is built first, and then the least favorable free-field deformation corresponding to the buried depth of the tunnel structure is treated as an equivalent seismic action. Then the critical seismic response of the tunnel structure can be achieved by calculating the integral tunnel-foundation model statically. Taking a certain shield tunnel structure in Beijing as the research object, the proposed method and accurate dynamic time-history analysis method were adopted respectively to obtain the longitudinal seismic response of the tunnel under SH wave incidence. The calculation results indicate that the proposed method has clear concept, simple process and high accuracy. Therefore, this suggested method can be introduced to seismic response analysis of linear underground structures under asynchronous seismic action.