Ta2O5 films are deposited on fused silica substrates by electron beam evaporation method.The optical property,x-ray photoelectron spectroscopy,band gap and nanosecond laser-induced damage threshold (LIDT) of the fihns before and after annealing are studied.It is found that the existence of an oxygen vacancy results in the decrease of the transmittance,refractive index,both macroscopic band gap and microscopic band gap,and the LIDT of Ta2O5 films.If the oxygen vacancy forms,the macroscopic band gap decreases 2％.However,when the oxygen vacancy forms the microscopic band gap decreases 73％ for crystalline Ta2O5 and 77％ for amorphous Ta2O5.The serious decrease of microscopic band gap may significantly increase the absorbance of the micro-area in Ta2O5 fihns when irradiated by laser,thus the damage probability increases.It is consistent with our experimental results that the LIDT of the as-deposited Ta2O5 films is 7.3 J/cm2,which increases 26％ to 9.2 J/cm2 when the oxygen vacancy is eliminated after annealing.