Abstract: CN_x films on silicon （111） wafer, quartz and Ti/C substrate with nitrogen concentration up to 20 at % have been prepared by a new plasma deposition technique, filtered arc deposition. The nitrogen concentration and area density of the films are measured by Rutherford back-scattering. The optical properties of the CN_x films are also characterized by ultraviolet-visible transmission and infrared reflective spectrometers. Results indicate that the optical band gap of the CN_x films is decreased with the increasing nitrogen concentration, accompanied with the reflectance increase of the films. Furthermore, the influence of N₂ partial pressure on the structure of the films with different nitrogen concentration is discussed.