For　to　solve　the　shortage　of　measuring　the　oil-film　in　roller　bearing,　this　paper　researches　the　ultrasonic　method　based　on　equivalent　stiffness.　It　also　discusses　how　the　character　of　transducer　affects　the　ultrasonic　oil-film　measurement,　and　takes　the　dual　element　transducer　and　immersion　transducer　to　do　the　experiment　respectively.　The　ultrasonic　method　is　feasible　to　measure　the　oil-film　thickness　from　the　experimental　results,　and　experimental　results　is　related　to　the　focus　spot　size.　Meanwhile,　the　ultrasonic　with　wide　broadband　and　narrow　pulse　is　conductive　to　oil-film　measure.