A CN/diamond composite structure on silicon substrate was obtained by a two-step technique in preparing polycrystalline diamond layers by microwave plasma assisted chemical vapor deposition and then CN films by reactive rf magnetron sputtering. The samples were annealed at different temperatures in the range of 200 to 800 degrees C, respectively. All the as-grown and annealed CN films, which fully covered the diamond underlayer with the formation of a rather adhesive interface, exhibited amorphous nature uniquely. X-ray photoelectron spectroscopy and energy-dispersive x-ray studies both revealed that the nitrogen concentration of the films decreases after annealed at high temperature. Infrared spectra also suggested the thermal modifications on the content and structure of the CN films. The electric resistivity varies in a large range as the annealing temperature increasing, and confirmed the bonding configuration in favor of a graphite-like structure at high temperature.