Abstract: The layered defects of seamless steel tube are caused by the further elongation of the non-metallic inclusions in the circular steel billet during rolling of the seamless steel pipe. The existence of the layered defect reduces the ability of seamless steel tube to bear the load, which causes stress concentration and affects the safe use of steel pipe. Phased array ultrasonic testing technology due to its own technical characteristics, has a high detection rate for layered defects, at the same time can image display defect appearance characteristics, and it is an effective method for layered defect detection.