In this paper, the constituents of essential oils which extracted with hydrodistillation from the herbal pair Flos Farfarae –Tatarian Aster Root (FF-TAR) and its signal herbs were analyzed by capillary GC-MS and elucidated based on the standard mass spectral data. 52, 44 and 45 kinds of volatile components were identified respectively. Relative mass fractions of the constituents were determined by area normalization method. The identified relative contents of essential oils were 96.48%, 88.47% and 91.61%, respectively. Four new volatile compounds in herbal pair Flos Farfarae –Tatarian Aster Root are produced because of the chemical reactions and physical changes occurred in the process of decocting two single herbs.