Taking into consideration the overlapping effect of electron clouds between two atoms in a molecule, a modification method is presented which can be used to calculate the total cross sections for electron scattering from numerous molecules at medium and high energies. The modified complex optical potential composed of static, exchange, polarization plus absorption is directly employed to calculate the total cross sections for electron scattering from isoelectronic molecules (HCl, H2S, PH3 and SiH4) over the energy range 30—5000eV using the additivity rule model at Hartree-Fock level. The obtained quantitative molecular total cross sections are compared with those obtained by experiments and other theories wherever available, and good agreement is obtained. It is shown that the additivity rule model together with the modified complex optical potential can give much better results than the unmodified one. So, the modification potential method presented here can improve the accuracy of the total cross section calculations of electron scattering from molecules.