Abstract: The SiO₂ antireflective (AR) coating was prepared by sol-gel method and then modified by plasma combined with hexamethyldisilazane (HMDS). The effects of treatment on the surface morphology, microstructure, optical properties, and laser induced damage performance are investigated to obtain the SiO₂ antireflective coating with good resistance to vacuum organic contaminants. The results show that the antireflection coating shrinks, the roughness decreases and the content of polar hydroxyl group decreases after plasma combined with HMDS surface modification. Plasma and HMDS surface treatment optimizes the structure and optical properties of the film. The hydrophobic capability of the film and the resistance performance to contaminants under vacuum conditions are significantly enhanced without bad effect on the high threshold of sol-gel silica antireflection coating.