Abstract: The principles of automatic ultrasonic testing technique (AUT) for pipeline welding were briefly introduced, including TOFD technology, phased array technology, and regional scanning method. The detection system and adjusting process was focused on. Based on the analysis of the actual testing results, AUT technology has shown great advantages in such as the testing speed, detection rate of area defect, accurate positioning and intuitive displaying, for the testing of long distamce pipeline with thick wall and the cross harbour turnel, and therefore has a broad application prospect. On the other hand, however, the AUT is not fit to manual welding primer or manual welding seam, and is showing some shortcomings such as high requirements for block, complex adjusting process, lack of guiding standards and expensive cost and so on.