Abstract: With an analysis of the relation between the aluminum honeycomb plate brazing joint and the ultrasonic C-scan detection method，an ultrasonic detection analysis model for the effective brazing joint connection area is established，on which a C-scan image is generated. Then，C-scan images are processed by the image processing methods such as image enhancement and edge detection. The processed images can clearly show the shape of the brazing joints. The actual measurement value of the brazing joint size is compared with the ultrasonic testing value，and the results show that the absolute errors of the effective connection area are less than 0.11 mm，which realized the quantitative automatic ultrasonic detection of the connection area for brazing aluminum honeycomb plate.