The spin polarization properties of organic/metal interfaces,which contains no magnetic atoms,is a very interesting subject in organic spintronics.In this article first-principles calculation are presented to study the adsorption of benzene molecule on the Cu(100) surface and the influences of the external electric field are discussed.Here,different contact configurations are selected.Our simulations show that an obvious spontaneous spin polarization oscillation generated in the benzene molecule when the electric field increased.The density of states,spin density distribution,as well as the differential charge density distributions are obtained.It is found that the spin polarization is come from the p-d orbital coupling between the benzene molecule and the electrode,which lead to the molecules energy level shift and the DOS broaden,so the two spin state near the Fermi level no longer equal to each other.The strength of the p-d orbital coupling oscillated with the electric field,so there are spin polarization oscillation in the benzene/Cu(100) interface when the electrical field changes.The results are favorable for the understanding of the spontaneous spin polarization characteristics of the organic/nonmagnetic metal structure.