Abstract: Ultrasonic phased array shear wave probe was used to carry out circumferential inspection on butt weld of high chromium alloy steel pipe with pipe diameter more than 300 mm and wall thickness more than 30 mm. It is found that there is a signal exceeding the standard for one to two times of wall thickness and the defect location depth and horizontal distance displayed by the testing instrument cannot be read directly, so it is difficult to judge the rejection directly according to the standard. The true defect depth and horizontal distance can only be determined through conversion. In this paper, formula calculation method, drawing method, simulation test block method, axial scanning method and film method were used to verify and identify the defect signal, and good results were obtained, thus avoiding misjudgment. It can provide reference for the signal recognition of the same kind of workpiece by ultrasonic phased array detection.