Abstract: In this paper, the conventional gemmological and spectral characteristics of a type Ⅱa colourless diamond sample were analyzed. Gemmological characteristics of the diamond sample were tested by gem microscope; The DiamondView^TM observed the growth structure and photoluminescence of the diamond sample; UV-Vis spectrometer detected the UV-Visible absorption characteristics of the diamond sample; Fourier infrared spectrometer determined the type of the diamond sample; The confocal laser Raman spectrometer and PL-3000 portable laser Raman spectrometer analyzed the characteristic spectra of defects in the diamond sample. Based on the analysis of experimental data, it is concluded that the diamond sample is natural Ⅱa type colourless diamond with the characteristic peak at 270 nm in UV-Vis spectrum, which provided complete laboratory appraisal basis, and enriched the instruction and guidance for special type ultraviolet absorption type of natural type Ⅱa diamond for daily testing.