Abstract: Aiming at the problem of defects in the bonding structure, the ultrasonic interface model and propagation path of the equal-thickness aluminum/aluminum bonding structure were analyzed.The pulse reflection signals of the bonded parts and the poorly bonded parts were obtained, and the simulated echo signals were constructed. The thickness of the bonding layer between the bonded and defective parts was changed and the amplitude of the fifth echo signal was correspondingly observed. The results show that the amplitude of the fifth echo of the poorly bonded part is significantly lower than that of the well-bonded area, and is not affected by the thickness of the bonding layer and the residual adhesive thickness. The fifth echo amplitude can be used as a criterion to judge whether there is a defect of poor adhesion in the bonding structure.