SO_2gas in the air has harmful effects on silk fabrics relics. In this study various silk fabrics samples were tested in 50μmol/mol of SO_2gas in air for various periods of time. Analytical techniques include chromatic aberration analysis, infrared analysis, amino acid analysis and xray diffraction (XRD) were usedto characterize the samples. The silk fabric sample underwent dry heat aging on 40℃ for 50days. It is concluded that the greatest change happens as the time increases:both the amino acids and the crystallinity of the silk fabric sample change in the presence of SO_2as the degree of aging increased.