Abstract: Recently，high－quality synthetic diamonds without revealing，as well as colour－altered diamonds，have entered into the market，which is very deceptive to consumers and brings great challenges to appraisal agencies.Therefore，the author carried a batch of diamonds through synthetizing and processing from a company on the detailed analysis of the tests，including magnification，luminous phenomena and spectral characteristics.Research results show that CVD synthetic diamonds and natural diamonds are almost colourless，and HPHT synthetic diamonds are yellow，with high clarity.The diamonds after irradiation treatment are blue，but their clarity is poor.Ultraviolet－visible spectra of CVD synthetic diamonds do not show any obvious characteristic absorption peaks，but ultraviolet－visible spectra of diamonds after irradiation processing display GR1radiation damage center.By the DiamondView^TMand the cathode luminescent instrument，blue fluorescence and lamellar growth structure are visible.It is difficult to classify the synthetic and natural diamonds by conventional identification methods.The characteristics of ultraviolet－visible spectra and fluorescence images under DiamondView^TMshould be combined to identify synthetic and natural diamonds.