Abstract: For the precise and simple determination of the maximym safety height of containing oil in vertical tank, the author makes a detailed analysis on such four factors that would influence the calculating precision. In the same time, he also points o it that there are same deficiency in the calculation of refe-rence1 and 2, thus he puts forward a calcolating formula for the maximUm safety height of containing oil and safety vol'me in vertical tank. Based on practi-sas and examples, it has been proved that this calculating method has such advantages as high precision and simple and practical application, and is su-itable to be used for various oil products, all kinds of tank and different con-dition of storage so that the safety of oil tank is ensured.