Abstract: When ultrasonic probe is used to detect curved workpiece, there are certain requirements for the clearance between the probe wedge and curved workpiece. Taking the tubular workpiece as an example, after analyzing the gap between the conventional probe and the curved wedge and the curved workpiece, the calculation formula of the gap was derived, and the adaptability of different wedges and workpiece was analyzed. First of all, the gap requirements in the ultrasonic testing standards for welds ISO 17640-2018, GB/T 11345-2013 and ASME BPVC V-2021 were compared. Then, the application of probe wedge in ASME BPVC V-2021 standard on curved workpiece was illustrated by an example. Finally, the minimum pipe diameter that can be applied by conventional probes to meet different standard gap requirements was calculated and compared, and the gap range between phased array curved wedge and the nominal pipe diameter was verified corresponding to the requirements of different standards. This research was helpful to correctly grind the probe and select the appropriate wedge in the ultrasonic testing of curved workpiece.