According　to　the　requirements　of　nuclear　safety　regulations,　nuclear　power　plants　must　be　equipped　with　seismic　instrumentation　systems,　which　are　mainly　used　for　monitoring　alarm　and　automatic　shutdown　alarm　during　an　earthquake.　Both　the　second　and　third　generation　NPPs　adopt　Peak　Ground　Acceleration　(PGA).　However,　among　the　seismic　acceleration　characteristics,　isolated　and　prominent　single　high　frequency　acceleration　peaks　have　no　decisive　influence　on　the　seismic　response.　Especially　when　the　earthquake　monitoring　alarm　is　at　1　out　of　7,　it　is　likely　to　cause　a　false　alarm　or　false　shutdown.　In　addition,　it　usually　takes　one　month　or　more　for　the　NPPs　to　restart　after　the　shutdown.　In　this　paper,　an　improved　seismic　instrumentation　system　based　on　the　existing　system　is　proposed.　For　high　intensity　areas,　three　components　resultant　acceleration　is　used　to　judge　the　2　out　of　4　logic　of　the　automatic　seismic　trip　system(ASTS).　For　low　intensity　areas,　the　seismic　failure　level　is　evaluated　quickly　by　using　three　components　resultant　acceleration,　seismic　instrument　intensity,　cumulative　absolute　velocity,　floor　response　spectrum　and　other　multi-parameters,　avoiding　unnecessary　and　long-term　shutdown　inspection.