Abstract: Water immersion ultrasonic testing technology uses water as a coupling medium and utilizes ultrasonic wave propagation characteristics to perform high-precision quantitative evaluation of objects. With advantages such as non-invasiveness and high sensitivity, it is widely used in multiple fields. In the nuclear industry, this technology is a key technique for ensuring the safe operation of nuclear power equipment. The key parameters of water immersion ultrasonic testing were systematically elaborated, with emphasis on its applications in the inspection of key components such as the reactor pressure vessel safety injection nozzle and pipe connection welds, evaporator heat transfer tube expansion transition sections, and container surface corrosion. Finally, future development directions of water immersion ultrasonic testing technology was prospected, providing references for further research and application of nondestructive testing technology in the nuclear industry.