In industrial production,it is required to measure the film thickness of the lubricating oil in the mechanical parts, and the ultrasonic testing can be used for the purpose of nondestructive testing.The piezoelectric transducer fabricated by aluminum nitride(AlN) ceramic membrane can realize the ultrasonic wave emission and reception.The AlN thin films are deposited on stainless steel by radio frequency magnetron sputtering technique.AlN thin film structure is characterized by Xray diffraction (XRD) and atomic force microscope (AFM),and the result is discussed.