Abstract: For Seismic have its own time-frequency localization characteristics,in other words,the energy is variable with time and frequencies.In this paper,according to the time-frequency characteristics of harmonic wavelet,the different frequency bands of the time varying energy expression was given by the ground motion of multi-scale wavelet transform,finally,a practical strong motion record which owned its time-frequency non-stationary characteristics has been analyzed,the results show that: not only seismic energy which distributes with the whole period of time at low frequency is smaller,but also energy attenuation is not obvious; seismic energy of intermediate frequency at the initial time is bigger with its rapid attenuation; seismic energy of high frequency is the biggest with the initial period,which decreases rapidly with time.The energy method in the paper provides a theory basis for structural design.