Abstract: The method of sawtooth pattern detection mode by common ultrasonic A wave applying to test crosswise crack of pipe welded joint might cause possibility of omission and misjudge. To prevent this from happening, the method of across welded joint mode by ultrasonic first reflection wave solved the problem preferably. Comparing with sawtooth pattern mode of paralleling with face of weld, the method of across welded joint mode can test existence of crosswise crack more easily, and the error of position caused by pipe radian can be corrected by calculation, the correction data corresponded to the original results. It is a positive and effective method of across welded joint mode for testing crosswise crack of thick walled heavy-caliber pipe welded joint in power plant.