Abstract: For simplified models of soil-structure interaction (SSI), frequency-independent impedance function is often adopted, which leads to relatively large calculation errors in the calculation of structural modal damping ratio. For two-dimensional SSI models, the influences of soil shear wave velocity, soil density, structural stiffness and structural mass on the dynamic characteristics of a single-degree-of-freedom superstructure are investigated. Based on the soil stiffness and damping coefficients derived by Luco, a correction function for the modal damping ratio of an equivalent single-degree-of-freedom system considering the effects of soil-structure interaction is established by comparing the modal damping ratios obtained from the complex modal identification solution and the Luco solution. The accuracy and effectiveness of the correction function are further verified through real-time coupled shaking table tests on a 2-story frame structure and seismic response analysis of a 5-story frame structure. The testing and numerical results show that the proposed modal damping ratio correction function can significantly improve the calculation accuracy of modal damping ratios.