Abstract: Taking single-layer double-span structure as the research object, the average response spectrum under variable damping ratio is established, and its regression analysis is carried out. The characteristics of the average response spectrum, that is, the horizontal seismic influence coefficient curve, are analyzed. The analysis shows that the average response spectrum is related to the surrounding rock properties, the frequency characteristics of seismic waves, the intensity of site forcement and the depth of the station. The shape of the relative response spectrum of variable damping ratio is different under different fortification intensities. The higher the fortification intensities, the lower the peak value of the response spectrum and the shorter the shape of the graph. When the surrounding rock parameters are changed, Poisson's ratio has the greatest influence on the change of the response spectrum, and the difference between the peak value and the shape of the response spectrum curve is the greatest. With the increase of burial depth, the peak value of influence coefficient of all kinds of site soil gradually decreases. The seismic influence coefficient obtained from the structural dynamic response caused by the spectral characteristics of seismic waves increases with the peak value of the Fourier spectrum of seismic waves.