The subway stations - bridge unitized (station - bridge unitized) projects can reduce urban traffic congestion and save construction space. But their seismic response mechanism and the seismic response of underground structures are not very clear. 3D models of station - bridge unitized condition and single station condition were established using finite difference software. Firstly, static calculations were completed, and the law of force and deformation of two conditions were analyzed. On the basis, with the input of El-Centro and Kobe waves, interlayer displacement angle, stress and weak positions of subway station were analyzed. Finally, the effects of load and height of the bridge on the seismic response of subway station were studied. The results indicate that as the input acceleration of bedrock increases, the effect of the overpass on the interlayer displacement angle and maximum stress of the subway station becomes greater. Tensile damage at the ends of station floors is easier to occur in station - bridge unitized condition, and the middle columns should also be attached equal importance to in strong earthquakes. There is a positive linear correlation between the interlayer displacement angle and bridge load, which can also be observed in bridge height. In addition, stresses increase linearly with bridge load and height.