Abstract: To detect the corrosion of CNG storage wells, we proposed a system for automatic ultrasonic test, which included collection of ultrasonic signal, analysis of corrosive data, display, storage and recognition. The hardware system included an ultrasonic transmitter and receiver card and an ultrasonic probe jig. The software was written in VC++, and Microsoft SQL Server 2000 was used for database. Our experiment showed that the system could effectively detect the defects in the sidewall of CNG storage wells.