Abstract: In view of the difficulties in the inspection of austenitic stainless steel small diameter pipe welding joint, a series of measures were taken, such as the development of special test block design, detection parameter optimization, detection capability verification, defect analysis and evaluation, etc. Based on this, a set of inspection process and evaluation methods of using phased array ultrasonic testing technology were summarized. This testing processes is suitable for quality evaluation of austenitic stainless steel small diameter pipe welding joint with outer diameter of 32~100 mm and wall thickness of 4~20 mm. The successful application in thermal power unit installation and maintenance engineering verifies the reliability and accuracy of the process, ensures the detection quality and effectively reduces the risk of radioactive source management and detection cost. The development of this detection technology provides a feasible technical scheme for phased array ultrasonic testing of austenitic stainless steel small diameter pipe welded joint.