The Ta2O5 optical thin films were deposited on glasses with the Ta2O5 as coating material by electron beam evaporation. The Ta2O5 optical thin films were annealed in air and argon atmosphere respectively. Measured the transmittance by spectrophotometer while the refractive index calculated by the minimum value of the transmittance. The structure of Ta2O5 optical thin films were measured by XRD. Optical properties of Ta2O5 optical thin films as a function of holding temperature, holding time and the atmosphere were studied. The results show that: the transmittances of Ta2O5 optical thin films are stable after 300～600 ℃/2 h annealing; the ultraviolet transmittance peak of Ta2O5 optical thin films are decreased, the visible transmittance peak and the refractive index increased after 400 ℃/(2 h,4 h) annealing in the atmosphere of argon; all the Ta2O5 films annealing at the temperature 300～600 ℃ are amorphous.