Abstract: The leakage monitoring system is used to monitor the integrity of the reactor coolant system pressure boundary (RCPB), and is also a prerequisite for the application of leak before break (LBB) technology. Leakage comprehensive diagnosis is the core function of leakage monitoring system. In this paper, the technical scheme of leakage comprehensive diagnosis is constructed from six aspects: system availability, data reliability, single meter leakage alarm, leakage comprehensive diagnosis, alarm response strategy and automatic calculation of leakage rate periodic test. The sensitivity and accuracy of leakage monitoring system are important performance indicators of the comprehensive leakage diagnosis technology, and also the key requirement of the integrity of RCPB and the application of LBB technology. Firstly, the conservative threshold range of triggering single instrument alarm is determined to ensure the sensitivity of detection. Then, the effective single instrument alarm threshold is checked and adjusted by the leakage comprehensive diagnosis technical scheme to ensure the accuracy of the alarm. Through theoretical calculation, data analysis and multi signal consistency judgment, the leakage monitoring system can timely and accurately diagnose the leakage. The intelligent of leakage diagnosis technology is fully applied to reduce the workload of review and alarm of operators.