Any　seismic　signal　can　be　decomposed　to　some　frequency　channels　by　multi-resolution　analysis.　Using　this　method,　earthquake　responses　of　MDOF　system　are　deduced　in　this　paper　and　seismic　signals　and　displacement　energies　in　distinct　frequency　channel　are　discussed.　With　the　examples　of　MDOF　system,　an　argument　that　in　elastic　system　total　earthquake　responses　can　be　obtained　by　adding　all　the　dynamic　response　contributions　of　distinct　frequency　channel　is　demonstrated　and　the　reconstructed　signal　after　restraining　high　frequency　is　applied　to　an　approximate　model.　With　the　energy　analysis,　the　signal　and　response　contributions　of　distinct　frequency　channel　are　clarified.