Dye analysis is important to the understanding of fabric color degradation and technical development of ancient printing and dyeing. In the present study, thin layer chromatography and Raman spectroscopy were used for the analysis of blue dyes from 6 silk fabric of Tang dynasty and decorative painting of Jian Fu Gong, Forbidden City. The applicability of these two methods in the cultural heritages was also studied. The results indicate that all these blue substances are indigo; indigo was not only used as dye in ancient fabrics, but also as pigment in decorative painting of historic building, so it is used widely. Both analytic methods have advantages and disadvantages; Raman spectroscopy is nondestructive analysis; thin layer chromatography needs small amount of sample, but could give more information.