Abstract: When calculating transfer coefficient on metallic oil tank wall by conventional method, it needs looking up a lot of charts and tables and course of try-and-error method, which fools a lot of time and results in deflection. Therefore, the large amount of charts and tables are fitted into curve equations by least square method so as to speed up calculation speed. The mathematical model of calculation of the transfer coefficient on the metallic oil tank wall is established and calculated by midpoint method, which improves the accuracy and speed.