In this paper, the seismic performance of a large subway station with a three-story, three-span major structure, and a two-story, three-span additional structure, was analyzed using a dynamic time-history method. The seismic responses of the site soil and the major structure under varying interaction modes and distances between major and additional structures were discussed. Under different working conditions, deformation of the site soil and the major structure, and the internal force and story drift angle of the major structure were analyzed and compared. Results showed that the influence of the neighboring underground structures-soil interaction on the site soil was more significant than that of the individual underground structures-soil interaction. When the distance between the additional structure and major structure was more than twice the structural width, the effect of the additional structure on the deformation of site soil around the major structure could be neglected, and the effect on the deformation and internal force of the major structure was essentially zero. Hence, the influence range of the interaction between neighboring underground structures under an earthquake was basically twice the structural width. The existence of the additional structure adversely affected the major structure under an earthquake. The deformation and internal force of the structure with a single-layer channel connection were smaller than those with double-channel connections.