Abstract: The various intermediates of elcctrophilic additions of F⁺,Cl⁺ to ethylcne,propene,fluorocthylene have been optimized by MNDOscheme with energy gradient technique.The most stable configurations were obtained.The substituted ethylenes tend to form the open intermediates more easily than the cthylene but the Cl⁺ as the reagent,tends to form the cyclic intermediate more easily than the F⁺.The interaction energies of the above three systems with F⁺ as electrophile have been studied further with ab initio method and Ewere decomposed into their components by Morokuma's decomposition scheme.In these reactions,it is found that charge transfer interaction is the most important one while the electrostatic interaction is the next.The effects of the substituting groups were also discussed.