The　influence　of　high　frequency　earthquakes　on　long-period　structures　and　the　transient　responses　of　such　structures　are　usually　ignored.　Using　wavelet　packets　transform,　the　transient　response　of　a　MDOF　system　is　calculated　based　on　harmonic　earthquake　response　analysis.　With　the　analyses　of　two　projects,　the　transient　vibration　patterns　of　a　long-period　building　due　to　high　frequency　ground　motion　are　eaxmined.　It　is　concluded　that　the　displacement　is　mainly　controlled　by　the　transient　response　in　low　order　modals.　In　high　frequency　earthquakes,　the　transient　displacement　of　a　long-period　structure　increases　with　the　building　height.　Therefore,　in　high　frequency　earthquake　the　maximum　displacement　of　a　long-period　structure　could　occur　in　transient　vibration　and　the　value　could　be　greater　than　resonance　vibration.　A　suggestion　is　made　that　the　ratio　of　natural　frequency　to　excitation　frequency　can　be　employed　as　the　index　of　criterion　for　long-period　structures.