Raman spectroscopy for studying of chemical vapor deposition (CVD) diamond is one of the most effective means. CVD diamond films with different grain sizes are analyzed by Raman spectrum. Ultraviolet Raman spectrum test shows that ultraviolet stimulated Raman spectrum effectively restrains the scattering of sp2 carbon and the non-diamond fluorescent background. The presence of 1140 cm-1 peak in the visible Raman spectrum attributed to the increase in quantity of trans-polyacetylene and the intensity enhancement of sp2 carbon scattering. Through the visible Raman spectrum detection, it is found that with the decrease of grain size, the intensity of 1140 cm-1 peak and 1460 cm-1 peak unceasingly strengthens, the intensity of the diamond peak constantly lowers, and the full width at half maximum (FWHM) of diamond peak continually broadens. The content of sp3 carbon decreases in the film. When micron diamond replaces cemented carbide as substrate material, the FHWM of diamond peak has greater decrease, and its intensity increases significantly. Impurity components in the films reduce significantly.