Abstract: In manufacturing for factories of hydraulic support, there exist the problems such as inefficiency and low reliability while inspecting the butt girth weld quality of hydraulic cylinder in traditional manual mode by using A-scan ultrasonic flaw detector. In order to conquer the disadvantages of manual ultrasonic testing and ensure weld quality, an ultrasonic imaging testing system was designed, taking digital ultrasonic flaw detector as base, computer as core, and existing automatic welding equipment as clamping workpiece platform. Then, general scheme, hardware and software structure of this system were introduced in detail. Moreover, the experimental verification of this system was carried out by using the sample of seamless steel tube containing artificial defects. Results showed that this system well realized automatization, digitalization and imaging of girth weld testing for hydraulic cylinder and laid a good foundation for automatic quantitative, locating analysis and intelligent recognition of flaws. The further improvement of this system and its application in manufacturing will considerably enhance efficiency and reliability of ultrasonic testing, and then effectively solve the problem of girth weld quality test for hydraulic cylinder.