Abstract: For underground water-sealing oil storages with large section, the cavern form plays an important role for the stability, durability and oil sealing capacity of caverns. In this paper, a certain project of underground water-sealing oil storage was taken as an example. NCAP-VEP numerical analysis was conducted on the cavern forms from the perspective of stress and displacement of surrounding rock. Numerical simulation was carried out mainly on three kinds of cavern forms (straight-wall arch, horseshoe arch and elliptic arch). And the pressure and tension applied on the surrounding rocks of each type of cavern were analyzed. It is considered from the view points of construction and operation that the construction of horseshoe arch cavern is more difficult than that of straight-wall arch cavern and it tilts towards inside the cavern at the lower part, so fire caused by falling rock occurs easily during its operation. Therefore, the straight-wall round or straightwall three-center arch is selected as the optimal cavern form.