“…Because the ultrasonic has advantages such as good directivity, strong penetrating power, high energy, and it can not be limited by checked material, so the ultrasonic detection method has become the focus in the coating thickness nondestructive testing.But due to the coating thickness is too thin, generally in micron, and it lead to the ratio between the ultrasonic wave and thickness is small, the coating ultrasonic of different interface echo affects each other, and make it more difficult to process the signal, therefore the applied base material thickness method is no longer applicable, it must design special ultrasonic testing system and information processing system.The ultrasonic thickness of coating methods mainly include pulse echo method [1], lamb wave method [2] and surface wave method [3], and so on. Pulse echo method is affected by the material surface roughness and the acoustic attenuation, and when the medium thickness is smaller than the double wavelength, the echo of medium surface will be mixed up together, so it is not easy to distinguish.…”