Abstract: After analyzing the drawbacks of the Jobacks equation for estimating △G_f~ ,a new theoretical formula is proposed.According to molecular orbital theory and taking into consideration the interactions among all the atoms of a molecule and restrictions in a whole molecule which depend on the electron effect,the author discovered the fact of relative independence of groups or bonds.By applying the matrix method,a semi-theoretical formula was derived.To check this equation,the data of 118 organic polar and 292 nonpolar compounds were used with an average error of 1.73% for 410 experimental values.This method is far better than the other methods reported in literature.