Abstract: There are various types of defects in diffusion welded joints of different metals. These defects seriously affect the integrity of the welded structure, and furthermore affect the in-service performance of the product itself. In this paper, we use ultrasonic scanning imaging technology to obtain the sample scanning pattern. Then based on the microstructure of the diffusion welding interface and on the ultrasonic signals, the raw material cracks, joint cracks, unwelded defects, and well-welded regions of the diffusion weld are characterized. By using nondestructive testing methods, the types, sizes, and positions of defects can be accurately evaluated.