Abstract: Polyethylene (PE) pipe has been widely used for the transportation of gas in cities because of its excellent corrosion resistance, good mechanical properties and longer service life. Fusion welding is one of the main connection methods of polyethylene pipe. On the basis of the research on the ultrasonic reflection of different type defects in the joint,the phased array ultrasonic technique is presented. An automatic ultrasonic testing system is designed and fabricated with phased array electronic focusing technique and real-time imaging technique,which is comprehensively to integrate impedance matching with acoustic coupling technique, with the purpose of overcoming the detecting difficulty caused by the attenuation of PE and transmitting loss at interface.The reliability and process performance are tested through detecting PE joints with typical defects. It is shown that the phased array ultrasonic technique presented in the paper is applicable for detecting typical defects in of butt fusion joint in Polyethylene Pipe.