Abstract: Since undisclosed CVD synthetic diamonds found in 2012, NGTC labs have detected various CVD synthetic diamonds with different properties.Some samples were identified to be CVD synthetic diamonds when they were submitted to Beijing lab (NGTC) in 2014.They are of special characteristics, which are different from the Gemesis type CVD diamonds, such as high silicon concentrations and weak or none fluorescence under SW UV light.Notably, these CVD synthetic diamond samples were characterized by fluorescence images that did not reveal CVD-special growth striations and phospherescence.In this paper, a heavily silicon-doped round brillant cut CVD synthetic diamond was investigated by UV-Vis, FTIR, PL and gemmological methods such as fluorescence under LW and SW UV light and DiamondView^TM.It was found that a CVD synthetic diamond showed photochromic effect.The colour, graded as I colour with slightly brown hue, temporarily changed to gray blue when illuminated under DiamondView^TM.Based on the analysis of the UV-Vis absorption spectra for the CVD synthetic diamond sample before and after being illuminated by SW UV light, it was found that the silicon concentration was high and the photochromic behavior was the transfer between(Si-V)^- and(Si-V)⁰defect.At the same time, the fluorescence and phosphorescence strength display some relationship with the concentration of(Si-V)^- defect.The silicon-doped CVD synthetic diamond with photochromic effect was identified in China for the first time.The labs should pay attention to this type of CVD synthetic diamonds.