Based　on　a　single-mass　model,　the　earthquake　responses　of　isolation　structures　with　different　natural　periods　were　analyzed　by　using　the　equivalent　linearization　method　and　the　time　history　analysis　method　according　to　China,　Japan　and　USA　codes.　Through　comparison　of　acceleration　response　spectra,　it　was　found　that　the　response　spectrum　of　the　long　period　part　of　the　design　response　spectrum　in　China　code　is　too　large.　According　to　the　results　of　time　history　analysis,　the　modified　equation　for　the　long　period　part　was　proposed　based　on　the　original　acceleration　response　spectrum.　Finally,　the　earthquake　response　of　an　isolation　structure　was　computed　by　using　the　new　modified　acceleration　response　equation　and　the　time　history　analysis　method,　and　the　results　obtained　with　the　modified　long　period　response　spectrum　were　consist　with　those　of　the　time　history　analysis.　The　response　analysis　results　showed　that　the　proposed　equation　of　response　spectrum　has　higher　analysis　precision　for　isolated　structures.