The ground states of styrene under different intense electric fields ranging from 0 to 0.05a.u. are optimized using density functional theory DFT/B3P86 at 6-311G basis set level. The excitation energies and oscillator strengths under the applied electric fields are calculated employing the revised hybrid CIS-DFT method. The results show that the electronic state，molecular geometry，total energy，dipole moment，and excitation energy are strongly dependent on the applied electric field. As the electric field changes from 0 to 0.02a.u.，many of the bond lengths of C—H increase，while some of the bond lengths of C—H decrease. However，further increase of the electric field strength results in a increase of them both due to the charge transfer induced by the applied electric field. As to the bond lengths of C—C，some of them increase，some of them decrease and some of them remain unchanged as the electric field changes from 0 to 0.05a.u.. The dipole moment of the ground state increases sharply with the applied field strength. With the electric field increasing，the total energy of the molecule decreases. The excitation energies of the first six excited states of styrene decrease with the increase of the applied electric field，indicating that the molecule is easy to be excited and dissociated under the electric field.