<p>Underground water-sealed caverns are critical infrastructures for China’s strategic oil reserves. Seepage control is highly stringent, and existing sealing techniques often fail to meet the requirements for managing water in water-rich fractured rock masses, thus failing to ensure the airtightness of the cavern. In this study, an underground water-sealed cavern project was used as a case study, with geological drilling, geological sketching, and advanced water exploration methods applied to assess the surrounding rock conditions and identify water-rich sections. Based on these assessments, a comprehensive grouting strategy based on the principle of “prioritizing pre-grouting, supplemented by post-excavation grouting, with multi-batch grouting” was proposed, and the grouting effect was evaluated using ground penetrating radar (GPR) and water pressure testing methods. Meanwhile, the theories of grouting in rock fractures were integrated with the practical techniques used in this project to analyze the mechanisms of slurry diffusion and blockage in the multi-batch grouting process. The research results indicated that advanced pre-grouting successfully filled most of the seepage channels within 20&#xa0;m ahead of the excavation face, resulting in a significant decline in the permeability of the surrounding rock. The water inflow was reduced by 62.67 L per minute (L/min) after pre-grouting, which achieved a reduction rate of up to 94%. Further grouting of the rock mass after excavation, with an increased number of grouting sessions, led to additional reductions in water inflow, with only minor seepage remaining. The research findings can significantly improve the sealing performance of underground water-sealed caverns, reduce water inflow, and lower operational costs in the later stages.</p>