Abstract: Oil and gas leak accidents easily occur in existing oil storage tanks for the double-sided corrosion and passive detection method. So a double-layer structure of oil storage tank was proposed in this paper. Computational fluid dynamics(CFD) methods were used to compare and optimize the two different bottom structures of oil storage tanks, the optimal parameters of the bottom structure met the demand of good flow uniformity and no stagnation zone was obtained. Furthermore, three dimensional numerical simulations were conducted on bottom structures with different locations of leak and inlet velocities (v) in order to get laws of outlet volume fraction (φ) and diffusion stabilization time (T) influenced by them. The results showed that the general tendency of leakage diffusion occurring in three different positions was roughly identical, that is, φ and T increased with the decrease of v, and the tendency became distinct when v decreased. The result of research has great significance for speeding up localization of double bottom structure of oil storage tank.