In this paper we established a comprehensive mathematical model to evaluate the conditions of safety and displacement system of the oil storage tank. The obtained theoretical solution was then analyzed by comparison with the actual storage data. The problem was addressed by step-by-step approach. Firstly, the cross-sectional method is used to establish a mathematical model for the relationship between theoretical oil capacity of the tank and the oil level height, for exsisting displacement and nonexisting displacement scenarios. Then, according to the actual oil level hight data, the corresponding theoretical oil quantity is obtained and compared with the actual oil quantity value, and a relative deviation between the two is evaluated. Taking the average deviation value as 3.371%, the correction function of the theoretical oil quantity is established. Then, the deviation function is applied to the nonexisting displacement scenario, and the relative error of the absolute oil output is calculated by comparing the values of the two adjacent moments. The calculation results verify the correctness of the correction function. Then, according to the corrected theoretical oil quantity and the actual oil quantity, the relation between the liquid level and the tank volume is analyzed. Finally, using MATLAB software, the tank capacity is calibrated according to the oil level height, with interval of 10 cm. The results are shown in Table1.