The composition and principles of the digital measuring system was investigated on the basis of digital oil measuring method. Fly attitude-oil quality - measuring height data tables were generated by using UG software calculation of oil quantity characteristics. Then the oil surface angle under different fly attitude and overload was calculated through coordinate transformation method. Finally the amount of oil was calculated by three-dimensional liner interpolation method. Meanwhile, the free surface movement of lubricating oil tank under different overload was simulated through VOF numerical model. The results showed that using UG software to build model and generate fly attitude-oil quantity-measuring height data tables is accurate and useful. The VOF model method is a complement to digital measurement, which can track the phase interface of continuum, analyze the movement of oil qualitatively and calculate the dead volume of digital method.