In this paper, the constituents of essential oils which extracted with hydrodistillation from the herbal pair Cortex Magnoliae Officinalis -Herba Ephedrae (CMO-HE) and its signal herbs were analyzed by capillary GC-MS and elucidated based on the standard mass spectral data. 44, 38 and 39 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 98.42%, 99.07% and 99.21%, respectively. It is further demonstrated that 28 and 25 volatile constituents of CMO-HE are from that of single herb CMO and HE, respectively. Ten kinds of new volatile compounds in CMO-HE are produced because of the chemical reactions and physical changes occurred in the process of decocting two single herbs.