Abstract: Aiming at the domestic L485 high strain ocean pipe with outer diameter of 559 mm and wall thickness of 31. 8 mm, different types and sizes of welding defects were made at different positions of the weld. Combined with the characteristics of full-automatic welding process, AUT(automatic ultrasonic testing) process was designed to test the sample pipe. The defects detected by AUT were sliced, the actual height of the defects were measured and compared with the detection results of AUT, which verified the detection accuracy and reliability of AUT detection process.