Abstract: Based on the relationship of shear wave velocity between the United States and China, 220 seismic records were selected from American PEER database and classified according to Chinese site classification. With the normalized method, the equivalent velocity spectrum of elastic signle degree of freedom (SDOF) systems was simplified into three portions based on a complex intensity index. The influence of the SDOF system parameters on the earthquake input equivalent velocity spectrum for five types of site soil was analyzed. The results show that the stiffness deduction coefficient has no effect on the equivalent velocity spectrum, and the peak and the declining stage of the equivalent velocity spectrum decrease with the increase of ductility coefficient and damping ratio, respectively. With the multiple fitting methods, the modified coefficients for the peak and the declining stage of the normalized equivalent velocity spectrum for elastic SDOF systems were proposed by considering all influence factors. Finally, the normalized equivalent velocity spectrum for inelastic SDOF systems was suggested, and the effectiveness was verified. This method can be applied to Chinese site soil and is also convenient.