Abstract: Addressing the characteristics of the oblique defects as occurring on the seamless steel pipe as hot-rolled with the CPE plug mill，a corresponding UT technical plan is worked out，involving such measures as adding 4° and 8° two-direction detection of both inner and outer artificial defects，adapting the oblique adjusting device as having equipped with 3 -D direction adjustment function，and equipped with the trimming self-lock mechanism，using the especiallyprepared immersion probe，focusing on the pipe concentricity when conducting the experimental detection，adjusting the water layer distance and the incident angle，and conducting the dynamic commissioning，and making the acoustic beam have a vertical relation with the artificial defect so as to significantly improve the detection accuracy.