Waveforcesactingontheoffshorestructureareofimportanceforthestructuredesignpointofview.Thereisasocalled'TwoTensionLegBuoyMooringSystem'designedtoopenuptheoilfieldinSouthChinaSea.Twobasesofthesystemaresittingontheseafloorof30-40metersdepthofwater.Inordertoconfirmthesafetyofthissystem,waveforcesareinvestigatedexperimentallyandnumerically.Nowadays,themeasuredmaterialsonthissubjectarescarce.InthemodeltestofDr.Chakrabarti,thetestset-upnecessitatedasmalluniformgapbe-tweenthemodelandtankfloor,andthecorrectresultsmustbecomefromanadjustment.Theauthorshavesolvedtheproblem.Inthepaper,twonumericalmethodsareadopted:3-Dboundaryintegralequationmethod)eigen-functionexpressionandmatchingmethod.TheformerconsistsofdistributionofHaskindGreen’functiononthebodysurface.Thelatter,however,bypidingthewholefluiddomainintosubregions,thevelocitypotentialforeachsubregionscanbedetermineduniquelybymatchingthevelocitypotentialontheircommonboundaries,whichwasexpressedformallybyitseigenfunctionexpansion.Asanexample,experimentalandnumericalresultsweregivenforacircularbaseinshallowsea.Theyagreequitewell.Althoughbothmethodsareeffective,thematchingmethodhasmoreefficiency.