Abstract: An analytical formula for the stress intensity factors of the compact tension specimens is derived from a simple mechanical analysis and can be applied to a very wide range of H/W and a/W. In comparison with the boundary collocation method, errors of its results are less than one percent （most of them-0.5 percent） The formula can be written as follows,where the fundamental functions Kb and Ks are obtained by fitting the data of Srawley and Gross. During fitting, it has been found that there are five K values incompatible with others among data given by Srawley and Gross. But they confirmed the recalculated results in the latter paper written by Fan Tinyou.The compliance of the specimens may easily be calculated from the formulas derived in this paper. The results are also found satisfactory.