We observed experimentally that at least two optical absorption peaks appear between 3500-6500? after bombardment of LiNbO3 crystal surface by low-energy ion. Also the relative dark conductivity increase by two order of magnitudes, the fact suggests that the additional optical absorption and conductiviting active center creates after ion-bombardment. During bombardment, owing to the prior sputtering of some atom and atom groups in the crystal, a substantial deviation of stoichiometry occur in the surface layer, which has a direct effect upon the optical and electrical properties of LiNbO3 crystal.The measurements of XPS (X photoelectron energy spectroscopy) prove that the structure of this surface layer conforms to the vacancy model of LiNbO3 defect structure. We propose a possible mechanism of the formation of this kind of active center in LiNbO3. By this model, we can explain qualitatively the result obtained from LiNbO3 crystals after bombardement by the mixed ions of Ar+/O+.