Abstract: JTUIS-Ⅳ ultrasonic testing system was developed by Xian Jiaotong university by using modern digital control, signal process and image process technology. The system could test the inside of switch gears without destroying to provide high quality C-scan image, and evaluated the image after scan. The experiment showed that the system had the advantages of good reliability, validity in nondestructive testing for brazed weldment of switch gears.