Abstract: As an important energy storage technology, underground water-sealed rock cavern oil depots are often associated with complex geological structures in their storage areas. Fault fracture zones, as an important component of these geological structures, have a significant impact on the operation of underground water-sealed rock cavern oil depots. Previous studies have mainly focused on the impact of fault fracture zones on the stability of the surrounding rock during the construction period of underground water-sealed rock cavern oil depots, with less attention paid to their influence on the seepage field during the oil storage period. In order to reveal the influence of fault fracture zones on the seepage field during the oil storage period of underground rock cavern oil depots, based on finite element numerical simulation software, the evolution of the seepage field during the oil storage period under the influence of fault fracture zones was analyzed. The variations in groundwater level, oil and gas leakage, and cavern water inflow under different dip angles and thicknesses of fault fracture zones were investigated, and a parameter sensitivity analysis was conducted. Suggestions were proposed for the site selection and fault treatment of underground water-sealed rock cavern oil depots. The results show that, compared with the case without a fault fracture zone, the cavern water inflow increases from 15.12 m³/d to 17.42 m³/d in the presence of a fault fracture zone, representing an increase of 15.21%. The presence of a fault fracture zone significantly affects the distribution of the seepage field during the oil storage period. The fault fracture zone alters the pattern of oil and gas migration, generates a non-uniform oil and gas leakage field, and exerts an inhibiting effect on oil and gas leakage. The groundwater level near the fault fracture zone drops more significantly, making oil and gas leakage more difficult. The magnitude of groundwater level decline during the oil storage period is positively correlated with the dip angle and thickness of the fault fracture zone. As the dip angle and thickness of the fault fracture zone increase, the cavern water inflow increases, resulting in higher operating costs. As the dip angle and thickness of the fault fracture zone increase, the inhibiting effect on oil and gas diffusion weakens, and the oil and gas diffusion range near the cavern becomes more uniform, resulting in greater oil and gas leakage. The interaction between the dip angle and thickness of the fault fracture zone is significant. The smaller the thickness, the greater the influence of the fault fracture zone dip angle, and the greater the variation in oil and gas leakage caused by a unit change in dip angle. Oil and gas leakage is more sensitive to changes in dip angle than to changes in the thickness of the fault fracture zone. When selecting sites for underground water-sealed rock cavern oil depots, fault fracture zones with large dip angles and great thicknesses should be avoided, with particular emphasis on avoiding faults with large dip angles to ensure water-sealing safety. It is recommended that the cavern be arranged so that its axis intersects the fault dip direction at a small angle. Reducing the permeability coefficient of fault fracture zones through measures such as grouting can effectively suppress oil and gas leakage. For fault fracture zones with unavoidable large dip angle and great thickness characteristics around the cavern, systematic grouting treatment should be implemented during the construction period to effectively control oil and gas leakage. The research results provide a theoretical reference for the site selection of underground water-sealed rock cavern oil depots and the operational management of the oil storage period under the influence of fault fracture zones.