Abstract: The main pipe of EPR (European Pressurized Reactor) nuclear power plant is an important component of connecting the main loop system of PWR nuclear power plant and is connected with forged austenitic stainless steel with narrow gap weld. The austenitic stainless steel pipe has the characteristics of acoustic anisotropy, coarse grain size and large wall thickness. In order to improve the reliability and efficiency of the ultrasonic inspection of MCL, phased array (PA) inspection technology has been investigated in this paper. The sound fields of the designed PA probes are demonstrated by the acoustic simulation software. Then, the phased array inspection technology was performed on the natural defects block. The results of the experiment indicated that the PA ultrasonic inspection technology could detect the defects of austenite welds effectively, and the precision of defects sizing met the requirements of related rules.