Defects like impurity, gas holes and loose connection in heat fusion joint or electro-fusion joint of PE (polyethylene) material, have brought potential safety hazard. Therefore professional ultrasound inspectors have been working on how to test defects within heat fusion or electro-fusion joints. With conventional UT (ultrasound testing) method, there are problems like serious attenuation of ultrasound echo in PE material and flaws not display directly so that it is difficult to apply conventional UT method. To make use of Phased Array (PA) characteristics like multi-elements, focusing and imaging, disadvantages of conventional UT can be avoided, and good testing effects may be achieved. By making heat fusion and electro-fusion joints samples with different defects, obtaining heat fusion and electro-fusion joints with different specifications at site, using PA probes with different elements and frequencies and adjusting parameters of PA systems, various experiments have been done for analysis. In this paper, examples will prove ultrasound PA can inspect defects in heat fusion and electro-fusion joints. There is phase transition line existing in heat fusion and electro-fusion joints. By measuring distance between phase transition line and fusion surface or un-welded pipe wall, connection quality can be determined. Keywords: heat fusion joint; electro-fusion joint; phased array (PA); phase transition line.