Abstract: An underground water-sealed oil storage is a kind of underground cavern with large cross section, and thesize of the cross section plays a critical role for the stability of the whole oil storage. In this paper, three cross sectionschemes (18 m×25 m, 19 m×28 m and 20 m×30 m) were analyzed at a fixed arch height. Then, based on numerical analysis, combined with the geological conditions and ground stress, 18 m×25 m was determined as the optimal cross section.Generally, an underground water-sealed oil storage includes several groups of cavern tanks composed of several parallelcaverns. No oil channeling is allowed between different groups of cavern tanks, so the spacing between two adjacent cavernsis particularly important for the stability of caverns and the isolation of oil products. Hoek-Brown model was adopted toanalyze the interaction of two adjacent caverns in three cross section schemes while their spacings were 2 times, 1.8 timesand 1.5 times the cavern span, respectively. The plastic zone at straight wall of cavern after excavation was provided to judgethe rationality of the spacing between cavities. The research results can be used as the guidance for engineeringpractice.