Abstract: Amorphous hydrogenated carbon nitride thin films (α-C_xN_y：H_1-x-y) were synthesized by external capacitive coupling low pressure plasma chemical vapor deposition (LPPCVD) with CH₄, N₂ and H₂ gases. The deposition rate and optical properties of the deposited CHN films were systematically analyzed as a function of radio power. The morphology of the films was investigated by scanning electron microscopy (SEM) and atomic force microscopy (AFM). The chemical structure and elemental composition of the CHN films were characterized by Fourier transform infrared spectroscopy ( FTIR). The FTIR investigation demonstrates the presence of carbon-nitrogen bonds with hydrogenated components in the films. And its optical gap ranges from 1.953-2.359 eV, and the optical gap becomes narrower with the incident power increasing.