Abstract: The success of large-scale water-sealed storage cavern lies in the construction of water curtain system. Water curtain system is used to enhance the sealing performance of the oil storage cavern by improving the water seal conditions around the cavern. After the completion of water curtain tunnel excavation, it is necessary to test the hydraulic connection of the water curtain system and then determine if more water curtain holes are required to ensure the water seal effect of the cavern. Taking the water curtain system construction of an underground oil storage as an example, this paper elaborates the preparation, test steps, data acquisition and interpretation of validity test for the water curtain system, and presents the comprehensive principles to judge the connectivity of water curtain system. Through comparing the measured value of pore water pressure under validity test and the theoretical value with water seal condition, the connectivity of the water curtain system is evaluated, and then the improving method of water seal effect is proposed, providing a reference for the industry peers.