Abstract: The risk of rust and explosion is raised when under ground gas storage well works for many years. This situation is very dangerous for around people. A detection device for security evaluation is developed. While taking off the coverage of the well, and full filling water into the well, the device which carry 81 sensors and consist of ultrasonic transducer array can be operated for rust detection. Digital signal processing is used for wall thickness of the well detection, such as stepped-frequency technology, transmitting pulse waveform modulation, digital amplitude equalizer and pulse compression technology. So, the detection sensitivity and resolution of wall thickness of the well is good.