Ta2O5 films were deposited by Ion Beam Sputtering (IBS) technique and they were annealed in air at the temperatures from 100 ℃ to 600 ℃ with a step of 100 ℃. Then the optical constants after annealing (refractive index, the inhomogeneity of refractive index, extinction coefficient and physical thickness), stress, crystalline and surface morphology were systematically studied. The experimental results indicate that with the annealing temperature increasing, the refractive indexes of the films decrease in the mass and the inhomogeneity of refractive index and the film thickness increase, by which the extinction coefficient and stress are improved. However, the crystal orientation and surface morphology of the films are no significant change. These results demonstrate that the thermal processing changes the characteristics of films but the thermal processing temperature for Ta2O5 films should be selected based on the application demands. These results will be a reference for parameter selection in Ta2O5 film deposition by the IBS.