Abstract: This paper considers the design basis and function of leakage monitoring system in nuclear power plants with VVER-1000. The process of the leak judgment and algorithm of leakage flowrate and leakage location are introduced. The scheme of acoustic model chart of the reactor coolant circuit is established and background noise in the reactor coolant circuit loop is obtained from calculation, and compared with the actual test results. The test bench of pipeline model is established and pipeline model is verified by the test bench. The correlation coefficient used to calculate the leakage flowrate and leakage location is obtained based on the test result. Through the design and verification of the acoustic leak monitoring system for nuclear power plants, the solid foundation is laid for the development of the online acoustic leak monitoring system for Unit 1 and Unit 2 in Tianwan Nuclear Power Plant.