The research shows that the accidents caused by seepage damage account for more than 20% of all the accidents of concrete gravity dams. The seepage safety state of concrete gravity dams has a great influence on the safety of concrete gravity dam. Therefore, it is very important to monitor and analyze the seepage safety of concrete gravity dams. After the completion of SL hydraulic project, the seepage of gravity dam body and foundation as well as the left and right banks is monitored and analyzed. The monitoring items include seepage flow of key parts, seepage pressure gauge and seepage around the dam. According to the analysis, the safety condition of normal operation of the dam can be checked and judged. It can help us test and judge the safety status of normal operation of the dam. The analysis results show that the anti-seepage system works normally at the dam and foundation, and the seepage flow tends to be stable, which conforms to the actual seepage law. The seepage monitoring design of SL dam is reasonable and can fully reflect the seepage situation at different parts of the dam.