Abstract: During the PSI or ISI in NPPs,the RPV stud must be inspected according to the ASME code section XI,and the best method for the volume inspection is ultrasonic test.This paper introduces the technology of scanning inside the central hole and scanning from the end surface of the stud,and details the block designing,apparatus choosing,signal cable selection,noise decreasing,probe designing,signal identification,defect evaluation and location technology.This technology can detect the flaw of 0.5 mm in depth on the thread area and screw area of the stud out surface.And the SNR can be 12dB higher.The location precision of axial is ±1mm;and the location precision of circumferential is ±2mm.Finally we developed the UT of RPV stud technology successfully,which are qualified and validated in fieldwork.