To improve the optical properties and laser damage threshold of TiO2 films and to ensure their wider use and greater stability in lasers, TiO2 films were deposited on K9 glass using electron beam evaporation technology, and the samples were post-treated with Ar/O mixed plasma. The effects of plasma post-treatment time on the laser damage characteristics of TiO2 thin films were analyzed by measuring the film spectral characteristics, surface defect density, surface topography, damage threshold, and damage topography. The experimental results showed that the refractive index and fill density of the films increased with increasing post-treatment time, whereas the physical thickness and surface roughness decreased. In addition, the surface defect density first decreased and then increased. After a 20-min post-treatment, the LIDT of the TiO2 film samples increased from 5.6 to 9.65 J/cm2 under a 1 064-nm laser irradiation, representing an increase of 72.3%.