Abstract: The geometric measurement method is generally used to calibrate the capacity of metal oil tank, that is, on the basis of dimensions of tank to be measured and measurement data obtained in relevent positions of tank and by a reasonable calculation, thus the tank capacity table (relation between the internal height and volume of tank) produces.About vertical tank, the calibration of capacity has a closed relation with the measurement data on internal diameter of each tank plate, internal height, oil volume of tank bottom, accessory volume within the tank and its original height as well as the degree of dip inclination; about horizontal tank, the calibration accuracy will be affected from the internal diameter of straight right cylinder, top plate, total height of dip hatch to tank bottom, degree of dip inclination, thickness of steel plate and measurement data of internal accessories of tank.