Abstract: Taking the horizontal tank as an example, hole leakage resource model and its numerical method for variable cross section tanks are studied. Based on Newton-Cotes formula and Simpson rule, parameters like random leakage time t and leakage rate u at leakage height h as well as leakage volume Q_m can be calculated by adopting compound integrated numerical method and VB software programming technique. On the basis of a continuous leakage case occurred in a horizontal tank, relation curves such as h-t, Q_m-t and Q_m-h are plotted using statistical software. It is considered that the study result not only breaks through limitations in conventional method to compute small hole leakage, but also provides a new method to study irregular leakage course of the tanks.