Abstract: In this paper, the tank displacement is divided into the horizontal displacement and the longitude inclination, assuming the angle of horizontal direction as β and the angle of longitude inclination angle as α, and the displacement identification on horizontal tank is also researched based on geometric relation. Horizontal displacement is analyzed from three aspects, that is, higher oil level, lower oil level and middle oil level. The paper analyzes the horizontal inclination of the oil tank which has been divided into the spherical body of two sides and the middle cylinder for easy analysis; for the cylinder part, a discussion on five cases divided for whether oil level of the right side contacts the side wall of the cylinder is conducted; while for the spherical body, the discussion over the two parts divided for bilateral spherical bodies—left upper and lower, right upper and lower, is made, and by this, calculus mathematical model for the corresponding relation between oil volume and tank level height is established. Referring to the measured data, this paper has worked out α and β in actual situations with least squares method and further given the tank capacity charts calibration of relevant tank level height and validated the correctness and reliability of the model.