Abstract: An improved hot-filament CVD system was developed to deposit diamond films. An infrared generator in the hot-filament CVD chamber was designed with the main wavelength 3.5 μm, which was right situated in the stretch vibration absorption peak of the C-H bond in methane molecule and H-H bond in hydrogen molecule. The decomposition of precursor gas is enhanced due to resonance absorption of energy, so high densities of hydrogen atom and active hydrocarbon cluster are obtained near the substrate surface. Therefore, higher growth rate (13 μm/h) and high quality diamond film are achieved.