Abstract: In order to get high capability titanium dioxide optical thin films, have synthesized by ion beam sputtering （IBS） and Ion Beam Assisted Deposition （IAD） at different vacuum degree. When the rate of oxygen increased, the value of vacuum degree is rising from 1.3×10^-4 Pa to 2.5×10^-4Pa. Spectrophotometer is used to test spectrum, the surface were characterized by scanning electron microscope （SEM）. When the vacuum degree decreased, it is found that the tiptop transmittance of titanium dioxide is increasing、the refractive index and the extinction coefficient are decreased and the surface quality changes roughness.When the vacuum degree is 2.0×10^-3 Pa, we get the best quality titanium dioxide optical thin film. The tiptop transmittance is 92%; The refractive index changes from 2.45 to 2.20;The extinction coefficient of the thin film is below 10^-4. Using Cauchy chromatic dispersion formula, the fitting curve accord well with the result by the envelope method, the formula of the refractive index change with wavelength is n（λ）=2.12+5.69×10⁴/λ²+8.07×10⁷/λ⁴.