The dispersivephasevelocityofawavepropagatingthroughasystemisanimportantparameterandcarriesvaluableinformationinnon-destructivetestsrelatedtomulti-layeredsystemssuchasasoilsite.The dispersivephasevelocityofawavecanbeestimatedusingthephasespectrum,whichiseasilyevaluatedthroughthecrosspowerspectrum.However,thephasespectrumasobtainedusingthecrosspowerspectrumissensitivetobackgroundnoise,whichalwaysexistsinthefield.Thiscausesdifficultiesinthedeterminationofthedispersivephasevelocities.Inthispaper,anewmethodtoevaluatethephasespectrumusingtheharmonicwavelettransformisproposed.Theintroducedmethod cansuccessfullyremovebackgroundnoiseeffects.Toevaluatethevalidityofthismethod,numericalsimulationsofmulti-layeredsystemswereperformed.Phasespectradeterminedbythesuggested methodwerefoundtobeingoodagreementwiththeactualphasespectraunderconditionscharacterized byheavybackgroundnoise.Thisshowsthepotentialoftheproposedmethod.