Abstract: The spent fuel pit transfer module is mainly a part of spent fuel pit of nuclear power plant, which is used to store fuel assembly materials and water. This paper outlines the monitoring of the leak rate of fluid water, predicts the leak rate range of helium gas leak detection through the conversion of gas and water leak rate, establishes the inspection area model, optimizes the inspection scope and process, finds the leak location quickly and accurately through the combination of range search and accurate search, and provides some experience for the leak detection of spent fuel pit.