Abstract: An ultrasonic testing system for the underground gas storage well was designed based on ultrasonic testing theory and through theoretical derivation and practical experience. This article theoretically analyzes the parameters, such as the eccentric distance of the circumferential ultrasonic testing and longitudinal ultrasonic testing, water thickness, radius of curvature, scan mode and so on, thus providing theoretical guidance and means to make the underground gas storage well ultrasonic testing system. In order to guarantee the stability of the dynamic testing probe position, a vertical center device has been designed to enable the testing probe to be in the centered position and to acquire the data reliably.