Abstract: The development of underground water-sealed caverns stays in a grim situation in China, since microfractures are induced at rock mass in caverns by oil transportation, oil pumping and water injection during the operation of oil storage in the caverns. Accordingly, the microseism monitoring technology is gradually presenting its unique advantages in evaluating the stability and safety of underground water-sealed caverns. Based on the analysis of micro-seismic activity events, the secondary activity of the fractures are described and the damage degree and safety status of the rock mass are diagnosed, so that the deformation mechanism of the rock mass is revealed. This paper presents the application of microseism monitoring technology in Jinzhou underground water-sealed oil storage cavern of PetroChina, in order to provide the reference for the development and management of future underground water-sealed oil storage caverns.