Abstract: The main problems of transmission ultrasonic method for co-cured composite sandwich honeycomb structure (CCSHS) are of signal dramatic attenuation and difficulty in determination of detected defect depth-location in skin or skin-core interface of CCSHS. In view of these problems, a high-resolution ultrasonic C-scan method, which was based on wide-band narrow-pulse ultrasonic reflection technique, was developed and used to NDT&E of CCSHS sandwiched defect quantitative evaluation. Testing and application results have demonstrated that high-quality time-resolved echo signals resulted from ultrasonic reflections in body of CCSHSs can be obtained. The signal amplitude difference between disbond and good-bonding zones is up to 11dB approximately. The distribution characterization of imaging grey resulted from disbonds, located in upper and lower adhesive film interfaces between skin-core, is obvious different from each other. Maximum deviation of detected disbond sizes by the C-scan is not larger than a single side length of the honeycomb. It provides an efficient and powerful quantitative NDT&E method for CCSHSs. A good practical application has been obtained.