Silicon oxynitride films were deposited by reactive pulsed magnetron sputtering. The optical, structural, and mechanical properties of silicon oxynitride films with different nitrogen proportions were analyzed via spectroscopy, atomic force microscopy, Twyman-Green interferometer, and nanoindentation. The refractive indices of the silicon oxynitride films were adjusted from 1.487 to 1.956 with the increase in nitrogen proportions. The surface roughness decreased from 1.33 to 0.97 nm with the increase in nitrogen proportions. The residual stress of the silicon oxynitride films was higher than for pure silicon nitride and silicon dioxide films. The hardness and Young's modulus increased from 13.51 to 19.74 GPa and 110.41 to 140.49 GPa with the increase in nitrogen proportions, respectively. The hardness and Young's modulus of antireflection coatings using silicon oxynitride film were 13.64 GPa and 102.11 GPa, respectively. Silicon oxynitride film could be used to improve the hardness of antireflective coatings.