-Thispaperpresentsacalculationmethodforthediffractionofbothregularwavesandirregularwavesofthesingledirectionalfrequencyspectrumbehindasinglejettywithatheoreticalanalysis,whichhasbeenconfirmedthroughthemodelexperiments,derivesamethodofcomputingthediffractedirregularwavesbehindthesinglejettywiththetheoreticalanalysisonthebasisofcomputationofthefielddataandgivestheformulasandthefiguresofthecomputationofwavediffractionsbehindtheverticalwallormoundsinglejetties.