To investigate the influences of soil properties and structural dimensions on the foundation coefficients in the response displacement method, the relationships between the foundation coefficients and elastic modulus of the soil, height-to-width ratio, burial ratio, and rock ratio of the structure were systematically analyzed. Then a simplified formula was proposed for calculating the foundation coefficients. The simplified formula was evaluated by applying it to the seismic analyses of subway stations under both homogeneous and layered sites, with comparative with the static finite element method recommended in the Code for Seismic Design of Urban Rail Transit Structures (GB 50909-2014). The research results show that the foundation coefficients exhibit a linear relationship with elastic modulus of soil. The height-to-width ratio of structure has a significant impact on the foundation coefficients of sidewall and bottom slab. Compared with the method in Japanese standards and the method modified by the width of slab, the structural internal forces calculated by the proposed simplified formula are more similar with those obtained by the method in Chinese code in both homogeneous and layered sites. It indicates that the proposed formulas have good applicability for calculating the foundation coefficients and can provide reference for seismic analysis of underground structures.