Abstract: The problem of interface debonding is a major hidden danger in operation of the vehicle. The experiment used longitudinal pulse-echo method, summarized the characteristics of three kinds of interface condition:there were obvious protruding crest at 48 mm and 52 mm when bonding well; when first-interface debond appeared, there was a large number of crest with 8 mm interval and high peak value; there was less crest with 8 mm interval and low peak when second-interface was of debond. Last, it was proven that length measurement and equivalent method as quantitative methods of interface debond defect was feasible when reasonable judgment benchmark was selected.