The internal stress and strain of chemical vapour deposition (CVD) diamond film deposited on silicon were observed and quantitatively determined by the bending beam technique and the X-ray diffraction peak broadening. The internal stress of the diamond film varies with the growth parameters during the deposition. The crystallinity and quality of the diamond film decline with increasing concentration of CH4/H-2, the result of which is the build-up of compressive stress. The compressive stress can be partly released by improving the diamond crystallinity of the film. For instance, the addition of argon to higher concentrations of CH4/H-2 can effectively enhance the concentration of hydrogen atoms and therefore increase the ratio of sp(3)/sp(2) which is required for a high quality of diamond film. It is interesting to note the variation in the morphology of the CVD diamond film synthesized at higher ratios of CH4/H-2 from a ball-like shape to a mixture of {111} and {100} facets and finally to {100} facets as the concentration of argon increases from O% to 33.3%.