Abstract: The cabin doors, wings, tail fins and other structures of the new aircraft extensively adopt large-thick composite honeycomb sandwich bonding structures. Based on the material composition and structural characteristics of the structure, the applicability of conventional ultrasonic reflection and penetration methods for detecting the bonding quality between honeycomb sandwich and panel is analyzed. It is found that both conventional ultrasonic reflection and penetration methods are difficult to detect debonding defects in large thick composite honeycomb sandwich structures. A detection method combining water jet coupled ultrasonic C-scan reflection method and contact coupled high-resolution focused ultrasonic A-scan reflection method is proposed. The proposed detection method is used to detect samples of large thick composite honeycomb sandwich bonding structures containing artificial defects. The detect results show that the proposed testing method can detect all artificial debonding defects at the I and II interfaces in the sample, with a detection sensitivity better than that of the Φ5 mm debonding, achieving ultrasonic detection of the bonding quality between 60 mm honeycomb sandwich and composite panel.