Abstract: The narrow-gap welding between the reactor pressure vessel nozzle safe-end and primary pipe in the first generation II plus NPP(nuclear power plant)is different from the wide gap welding in Ling Ao Phase II NPP.For this different structure between the two NPPs,based on the results of qualification results of Ling Ao Phase II NPP,supplement qualification for narrow-gap welding inspection is required.The narrow-gap welding inspection qualification is a comprehensive qualification.That is the testing procedures include both technical justification and practical test.Visualization of laser ultrasonic detection technology and computerized ultrasonic simulation were used in qualification as one or two methods for technical Justification.Focused on the study of ultrasonic inspection technology,sound field distribution,ultrasonic responses to the defects in the weld,as well as ultrasonic beam propagation were tested and it demonstrated that the designed inspection process could meet the actual inspection requirements.Finally,through actual inspection using real narrow gap welding test block containing defects,it was validated that the designed ultrasonic technology is reasonable and applicable.