Statistic　and　theory　based　methods　are　mainly　used　for　predicting　earthquake　input　energy.　Statistical　energy　spectrum　methods　need　abundant　time-history　simulation　and　are　lack　of　solid　theoretical　basis,　while　theoretical　prediction　methods　are　derived　from　structural　dynamics　with　necessary　assumptions,　so　that　these　methods　have　relatively　low　accuracy　resulted　from　their　assumptions.　In　this　work　the　comparison　of　simulation　and　analysis　showed　that,　due　to　the　influence　of　structural　transient　response　ignored　by　existing　theoretical　prediction　methods,　more　than　40%　errors　exist　in　prediction　of　earthquake　input　energy　for　structures　with　low　damping　ratio　and　long　period.　Based　on　Fourier　decomposition,　a　new　theoretical　method　was　proposed　for　earthquake　input　energy　prediction　considering　the　influence　of　transient　response.　The　comparative　analysis　show　that　the　proposed　method　significantly　improves　prediction　accuracy　of　earthquake　input　energy.