Abstract: A mixture of H₂, CH₄ and Ar gas was used as feed gas under gas recycling condition. Diamond films with different thicknesses were deposited on molybdenum substrates by a 100 kW DC arc plasma jet CVD system at 850 and 950℃. The morphology, quality, orientation and residual stress of diamond films were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. The results show that the quality of diamond films increases and the residual stress in diamond films decreases with increasing film thickness at 850℃. Diamond films with good growth stability were obtained and the tensile residual stress in diamond films was observed. The diamond film of 110μm in thickness deposited at 850℃ has a better growth stability, a higher quality and a smaller residual stress than the diamond film of 120 μm in thickness deposited at 950℃ when the flow rate of reaction gases is kept unchanged.