Theharmonicanalysismethodbasedonhighandlowwaterlevelsisdiscussedinthispaper.Inordertomakefulluseoftheinformationofhighandlowwaterobservations(thetimederivativeofwaterlevelattheobservationtimeiszero),theweightcoefficient,w,isintroducedtocontroltheimportanceofthepartrelatedtothisinformationintheerrorformula.Themajordiurnalconstituents,O1andK1,andsemi-diurnalconstituents,N2,M2andS2areselecteddirectlyfromthemonthlydataanalysis,andsomeotherimportantconstituents,P1,v2andK2,areincludedastheinferredconstituents.Theobtainedharmonicconstantsofthemajorconstituentsareveryclosetothoseobtainedfromtheanalysisofhourlydata,andthisshowsthathighandlowwaterdatacanbeusedtoextracttidalconstantswithhighaccuracy.Theanalysisresultalsoshowsthattheinferenceandtheweightingcoefficientareimportantinthehighandlowwaterdataanalysis,anditissuggestedthatw≥1shouldbetakeninmonthlyhighandlowwaterdataanalysis.Thisanalysismethodcanbeuseddirectlytoanalyzealtimetricdatawithw=0.
