Abstract: Automated water-immersion ultrasonic detection equipment for large-diameter pipe is consist of testing host, roller mechanical transmission system, electric control system, water system, ultrasonic flaw detector and computer system. By using water-immersion way and by generating S-waves for fully scanning, the equipment can be used to identify and then discriminate flaws by the ultrasonic flaw detector, and finally the computer can record the defect size and alarm. Thus it is able to meet the requirements of ultrasonic automated testing.