Abstract: The advantages, inpection principle, probe assemblage and distribution, test block and artifical defects distribution, result presentation, inspection steps and defect evaluation method of the automatic ultrasonic testing(AUT) were introduced by taking a submarine pipeline installation project as an example. According to the comparision of the AUT and macro results of the same defect, it could be proved that the AUT had a relatively high precision in defect locating and sizing. Combining to engineering ctritical assessment(ECA), the welding quality of submarine pipeline girth weld could be properly and accurately assessed and controlled. It was significant for ensuring the welding quality of submarine pipeline girth weld and reducing the cost of the pipeline installation.