Etching treatment was performed on glass surface by dissociated nitrogen using anode layer linear ion source. The changes of glass surface after surface modification was analyzed and the effect of ionization voltage on surface roughness, refractive index and optical thickness was investigated. Accordingly, the relationship between Δ spectral characteristics of fixed wavelength changed angle of incidence and refractive index, Brewster angle, surface roughness and optical thickness was discussed through the comparison of Δ spectrum under different surface conditions based on spectroscopic ellipsometry. The results show that the shape of Δ spectrum near Brewster angle changes, the abrupt change of Δ spectrum shifts to larger angle, and the slope of Δ spectrum increase at the same time. Modeling and fitting analysis reveals that an optically denser layer was produced, the refraction index and Brewster angle increase and surface roughness decrease of glass caused by nitrogen ion beam etching treatment. However, the refraction remains consistence, and the depth of denser layer increase with increasing ionization voltage. The surface morphology analysis by AFM verified the leveling effect of glass surface by nitrogen ion beam. XPS measurement indicates the optional sputtering of glass surface by nitrogen ion beam, inferring the generation of denser layer arises from the compaction of ion beam. Furthermore, the general relationship between the characteristic of Δ spectrum and surface conditions of materials was theoretical derived and verified, and an evaluation of material surface variations was proposed. Such as the increase of abrupt change angle illustrates the increase of refractive index and Brewster angle, the increase of slope demonstrates the decrease of surface roughness, the increase of sharp corner of both sides evident the increase of optical thickness, vice-versa.