Abstract: At present, the diaphragm wall is always used as the partial side wall of the underground subway station. However, the diaphragm wall is always neglected in the seismic design of an underground structure for that it is looked as a reserved safety for its earthquake resistance. To verify this opinion, a finite-element model is established to simulate the static and dynamic coupling interaction among the soil, the diaphragm wall and the underground subway station. The effects of the diaphragm wall on the earthquake responses of the underground subway station are investigated and analyzed. As a result, the diaphragm wall can increase the lateral deformation stiffness of the underground structure, which reduces the relative lateral seismic deformation of the underground structure. From this point, the seismic design method for the underground structure is conservative. However, the diaphragm wall may also change the seismic deformation characteristics of the underground structure, which will aggravate the earthquake-induced tension damages of the plates of the underground structure under strong earthquakes. Moreover, the diaphragm wall may affect the friction responses on the interaction surfaces between the soils and the underground structure.