Generally,thereliabilityofami-slidingandanti-overturningstabilityofanisolatedgravitycylinderinacertainworkingperiodcanbeevaluatedonlywhenthestatisticalpropertiesofshorttermstabilityaregivenfirst.Theauthorsusednumericalmethodtosimulatethestabilitystatefunctionofacylinderinshort-crestedsea,andfurthertogettheprobabiliticalcharacteristicsofthestructure’sstabilitybytimedomainanalysis.Theexternalloadsappearedinthestatefunctionsincludehorizontalwaveforce,liftforceandtherespectivemoments,andtheloadsarecorrelatedbyco-spectrum.Thenumericalmethodpresentedinthispapercanbeusednotonlytosolveshorttermreliabilityproblemdirectly,buttocalculateandanalysethelongtermreliabilityproblemaswell.Forcircularcylinders,anexampleofsimulationandanalysisisdisplayedinthispaper.