In this study, the blue dyes from a group of Chinese ancient silk samples, which include a Qing Dynasty fan cover, a blue Cotton-padded jacket and a Yuan Dynasty baina pillow top excavated at Gezidong were analyzed by Micro-Raman spectroscopy (Micro-Raman), thin layer chromatography (TLC), UV-visible absorption spectroscopy (UV-Vis) and high-performance liquid chromatography (HPLC). The results showed that all the blue dyes were indigo, their composition being indigotin and indirubin. Because of the difference in manufacturing processes or degree of ageing, the ratios of indigotin and indirubin were different. Indigo samples were artificially aged by UVA light, at high temperature (50[degree]C) and humidity (RH=85%), and the samples were tested before and after aging. After aging in ultraviolet light for 2 months, the relative content of indirubin decreased significantly. After aging at high temperature and humidity for 6 months, both indigotin and indirubin contents were reduced. At high temperatures the ratio of indigotin to indirubim was reduced, suggesting that indigotin was more sensitive to heat than indirubin. The blue plant dyes were effectively characterized using non-destructive and less invasive technologies. The mechanism of degradation of indigo dyes was proposed based on the aging test. This study is of importance for research on dyeing process research and color conservation.