Abstract: The optical properties of TiO₂thin film deposited by electron beam evaporation with different oxygen flux were studied.When the oxygen flux from 37.4×10^-3Pa·m³·s^-1to 61.2×10^-3Pa·m³·s^-1,vacuum degree was rising from 1.4×10^-3Pa to 2.5×10^-3Pa,the different optical properties will gain from TiO₂thin film.Spectrophotometer was used to test spectrum,when the vacuum degree decreased,it was found that peak value transmittance of TiO₂has increased.The refractive index and extinction coefficient increased first and then decreased.Under vacuum degree of 2.0×10^-3Pa,the best TiO₂thin film quality,the peak value transmittance was 92%,the refractive index changed from 2.50 to 2.20.The extinction coefficient was below 10^-4.By-use Cauchy chromatic dispersion formula.The fitting curve accorded well with the result by the envelope method.Refractive index changing with the wavelength formula is n(λ)=2.17+6.12×10⁴/λ²+2.98×10⁸/λ⁴.