Basedonthetheoryofcouplingvibrationandflexuralvibrationofthinrodofrectangularcrosssection,thefiexuralvibrationofrectangularthinplatewasstudied.Thefrequencyequationwasderivedundertheconditionoffreeboundaries.Thenormalmodesandtherelationbetweenthenormalmodesandtheresonantfrequencywereobtained.Experimentsshowedthatthecalculatedresonantfrequenciesagreewellwiththemeasuredresults,andtherectangularthinplateinflexuralvibrationhasabundantresonantfrequencies.Theradiatorofflexuralvibrationusedinultrasoniccleaningandothertechniqueshastheadvantagesoflargeacousticradiatingarea,uniformacousticfieldandeasyadjustmentofresonantfrequencies,provingthatitisapromisingultrasonicsource.