Abstract. Cumulative energy response spectra can generally be used to estimate earthquake energy demand of structures. Some research findings show that the earthquake input energy demand is stable than other forms of energy demand, so it is important for scholars to research earthquake input energy demand and establish earthquake input energy spectra. For the purpose of obtaining the mean spectra, earthquake input energy is normalized as the ratio of earthquake input energy to square of peak ground acceleration. The energy balance equation is established based on the SDOF system, and the improved earthquake input energy spectral model is presented. The earthquake motion records of three kinds of soil sites are selected as the earthquake excitations of the SDOF system, and the mean spectra is established by nonlinear time history analysis. The influences of natural period, ductility factor and soil site on earthquake input energy are analyzed.