An electrostatic three-center model with four parameters r_m, q, ΔE and r for diatomic bonds was proposed, based on Hellmann-Feyniman theorem with some additional assumptions.Equations relating these four parameters with the effective nuclear charges and covalent radii of the atoms were derived.Molecular properties such as dipole moment, force constant, field gradient at the nucleus and nonlinear snscepti bility can be calculated in terms of these parameters.The results of calculation ase baeioal in agreement with experimental values.