Abstract: With the continuous expansion of national strategic reserve scale, less massive crystalline rock mass is available in China due to the limitation of various factors. Therefore, making a breakthrough in the construction technology of an underground water-sealed cavern in sandstone area can greatly broaden the site available for the underground caverns. In order to study the feasibility of cavern construction in sandstone area, the seepage field models of underground caverns in sandstone area under three working conditions of horizontal bedding, inclined 10° bedding and inclined 50° bedding were established with the FEFLOW software under the background of site selection for cavern construction in a sandstone area in southwest China. It is assumed that 2 to 3 layers of thick mudstone exist in the sandstone to amplify the damage degree of low-permeability mudstone layers to the water-sealed environment, so as to better study the design technology of water seal for the underground caverns in sandstone area. The simulation results show that the thick mudstone layers have the least influence on the inclined 50° bedding and the greatest influence on the horizontal bedding. The thick mudstone layers, as the water barrier in the groundwater environment, seriously affect or even destroy the water-sealed environment. By adjusting the model in a targeted way such as setting horizontal water curtain holes and a vertical or oblique water curtain system, the water-sealed effect is improved obviously. In the actual project, water seal can be realized by moving down the horizontal water curtain system, or setting a vertical or oblique water curtain system in specific areas. The results can provide theoretical reference for the design and site selection of underground water-sealed caverns in sandstone area.