Abstract: Based on definite integral method, the formula to calculate the volume of small ellipse oil tank and actual oil tank under the respective condition of displacement-free and displacement of tilt and deflection is deduced, and the displacement parameters are identified by least squares. Based on the data in Title A of China Undergraduate Mathematical Contest in Modeling (CUMCM) 2010, the tank capacity table of two above oil tanks after displacement of tilt and deflection are calculated. By analyzing the tank capacity change principle before and after the displacement, the obvious influence of longitudinal tilt on the tank capacity table of oil storage tank is confirmed, which prove that the approximate algorithm of oil volume is stable and feasible after the displacement. The research result provides positive effect in strengthening of oil metering and loss management, which reflects the general significance and application value in the engineering.