The standard "GB/T 18329.4-2021 Sliding Bearings, Multi-layer Metal Sliding Bearings, Part 4: Bond Mass Ultrasonic Penetration Nondestructive Testing of Alloy Film Thickness ≥ 0.3mm" specifies a method for detecting the bond mass between the alloy layer and the backing of the bearing by means of the liquid immersion ultrasonic penetration method. It is suitable for a variety of sliding bearings with alloy layer Film thickness ≥ 0.3 mm and inner diameter ≥ 40 mm, including rectangular sliding bearings with non-blue bushes, bushings, thrust flanges and plane guides. The method qualitatively evaluates the bond mass by analyzing the signal strength of the ultrasonic penetration of the backing and the alloy binding surface. The standard does not apply to specific structural areas of the sliding bearing, such as chamfers, oil holes, etc.