Inthispaperthe0-1combinedBEMisadoptedtosubpidethecomputationaldomainboundary,andtodiscretizetheGreen’sintegralexpressionbasedonLaplaceequation.TheFEMisusedtosubpidethewavesurfaceanddeducethesurfaceequationwhichsatisfiesthenonlinearboundaryconditionsonthesurface.TheequationswithpotentialfunctionandwavesurfaceheightasanunknownquantitybyapplicationofTaylorexpansionapproachcanbesolvedbyiterationwithinthetimestep.Inm-timeiterationwithinthecomputationalprocessoftimestep(n-1)ΔttonΔt,theresultsofthepreviousiterationaretakenastheinitialvalueofthetwo-orderunknowntermsinthepresentiteration.Thus,animprovedtrackingmodeofnonlinearwavesurfaceisestablished,andnumericalresultsofwavetanktestindicatethatthismodeisimprovedobviouslyandismoreprecisethanthepreviousnumericalmodelwhichignoredthetwo-orderunknowntermsofwavesurfacelocationandvelocitypotentialfunctionincomparisonwiththetheoreticalvalues.