A　localized　fault　such　as　tooth　crack　excites　transients　into　the　background　vibration,　which　results　in　a　sequence　of　sideband　components　in　the　spectrum　which　include　both　amplitude　modulation　and　frequency　phase　modulation.　Cyclostationary　demodulation　method　provides　an　effective　alternative　for　this　type　fault.　This　paper　concerns　with　the　effectiveness　of　the　cyclic　autocorrelation　function　and　the　degree　of　cyclostationary　function　in　frequency　modulated　signal　and　amplitude　modulated　signal.　By　systematically　analyzing　and　comparing　these　two　effective　approaches　with　simulation　signals　and　practical　vibration　signal,　both　the　advantages　and　disadvantages　of　each　method　and　their　application　conditions　are　given　respectively.