Ta2O5 is widely used as a kind of high refractive index film material.The optical constant is vary because of dispersion and absorption as well as different technological conditions.A kind of using electron gun of fabrication of thin film evaporation and ion beam assisted method is introduced.The test based on the Cauchy model of the films in the near ultraviolet to near infrared optical constants are fitted,and illustrates the application of the material in short wavelength pass filter.