A study has been conducted into the dyeing of silk fabric in supercritical carbon dioxide. In order to reach better dyeing effect, plasma modifying is used to silk. Plasma modifying can decompose disulfide bond of the protein fiber, change the state of scale layer and break silk gum of fiber so that dyestuff could infiltrate. Factors of plasma modifying are fixed, including pH value, processing time. And they affect the values of fabric colour feature and fabric strength. In this work, C.I. Disperse Blue-77 and C.I. Disperse Yellow E-3G are used by combining orthogonal experiment and single factor analysis. During dyeing process, temperature and pressure have a great impact on the result. Modification process and dyeing process are optimized, and the best process is determined. The results presented in this study show dyestuff can infiltrate through modified fabric easily. Through the testing, the washing fastness and rubbing fastness of silk fabric after being modified are improved. The changes between before and after dyeing are analyzed by scanning electron microscope and infrared spectrometer. It is showed that modified fabric obtains a better effect.