Abstract：Three design schemes and one real tank with a same volume but different thickness and height at various parts are compared. The 1.5 Mm3 crude oil tank is analyzed with the nonlinear finite element software ABAQUS. The stress distribution in the whole tank is calculated. An optimized scheme is chosen according to the calculation results. The stress distribution is evaluated based on the design standard of pressure vessels. The calculation shows that the tank is safe with stored crude oil. Except the upper and down parts, the stress on the wall is uniformly distributed at a high level. The highest stress is found at the down second part of the wall. The stress on the bottom plate is low. But the stress at the welding inner corner between wall and bottom plate is higher than the permitted stress level. When the stress is properly classified, the standard requirements can be met.