Abstract: It′s difficult to detect the cracks at special weld structures. Therefore, this paper proposes an ultrasonic phased array “fan sweep angle region analysis method” to determine defects. At the same time, computer simulation technology is used to guide the development of ultrasonic phased array detection technology, the method can effectively guide the design of the ultrasonic phased array detection process, visually display the coverage state of the ultrasonic beam in the pipe joint, and overcome the blindness of the phased array ultrasonic detection parameter setting. It can provide reference for the nondestructive detection of the crack at the special structure.