In heat treatment experiments, red corundum samples before and after heat treatment are analyzed by UV-VIS absorption spectra. Under the heat of 1 350~1 580 ℃, oxygen gas atmosphere, Al(OH)3 and anhydrous borax as fluxs, the parti-colour of the samples such as purple, or yellow are declined with purer red. The inclusions melt and diffuse by heating; the flux can be filled with fissures in higher transparency. Thus Yuanjiang red corundum can be changed into a more perfect ruby by the heat treatment.