Abstract: Automated ultrasonic testing (AUT) method is often the first choice on inspection of the girth welds of the subsea pipeline because of its advantage of efficiency, accuracy and environment-friendly behavior. According to the AUT standard, the AUT system should meet the requirement of system qualification test before its application to the inspection of the girth weld of the subsea pipeline, for which the macro sectioning plays a key role in the AUT system qualification. In the macro sectioning, 6 test coupons (58 defects in total) with the dimension of OD of 508 mm, WT of 31. 6 mm & 28. 4 mm, respectively, have been manufactured. The method of macro sectioning includes: defect identification, scribing the lines, macro section, surface preparation, marking and photographing. Eventually, with the comparison between AUT data evaluation and macro section, the defect height sizing accuracy of AUT system can be qualified.