Abstract: The diamond films were prepared by hot filament chemical vapor deposition.Trace rare gases optical emission spectroscopy (OES) was used to measure the active species during the diamond growth.The quality and morphology of grown diamond films were characterized by SEM and Raman spectra.When the other parameters were kept constant, with the increasing gas flux of the carbon source, the electron temperature generally decreased.However, if the carbon source flow was between 50cm³/min and 70cm³/min there appeared an abnormal situation, which was to first increase and then decline, maximum peak at the vicinity of 60cm³/min, when the charged particles reached the substrate with the maximum flux and energy.Meanwhile, the content of carbon-containing groups, such as CO, C₂ and CH, was at there minimum value near vicinity of 60cm³/min minimum.Vapor depositing process went towards the direction to grow diamond film, with maximum growth rate.However, the quality of diamond films decreased as the concentration of carbon source increased.