Based　on　wavelet　transform　and　harmonic　earthquake　response　analysis,　transient　response　as　well　as　its　response　spectra　of　SDOF　system　are　discussed　by　multi-resolution　analysis　and　linear　amplitude　modulation.　It　is　concluded　that　the　transient　response　to　a　seismic　signal　can　increase　greatly　in　the　displacement　response　of　structures,　particularly　for　the　structures　with　long　periods.　Therefore,　transient　response　should　not　be　ignored　in　earthquake-resistant　design.