Objective To investigate the changes in main essential constituents in Atractylodes macrocephala and Ramulus cinnamomi and their herbal pair,further providing basis for getting the pairing rules of Traditional Chinese Medicine and unveiling novel bioactive constituents. Methods The Essential constituents were extracted from Atractylodes macrocephala and Ramulus cinnamomi macrocephala and their herbal pair by employing the steam distillation,measured by GC-MS and the overlapped spectral peaks were analyzed by chemometric resolution method (CRM) ; temperature-programmed retention indices were employed for qualitative analysis. Results Totally 29,66 and 55 Essential constituents were identified from Atractylodes macrocephala and Ramulus cinnamomi and their herbal pair respectively,accounting for 95. 93% , 94. 43% and 96. 35% of total essential oils correspondingly. Single herbs and their pair had four common constituents,accounting for 13. 14% of total essential oils. After processed in the herbal pair,four new constituents were identified from the herbal pair; 33 constituents were not identified from Ramulus cinnamomi and 7 were not found from Atractylodes macrocephala. The main Essential constituents in herbal pair were 2-( 2-Methoxyphenoxy) phenol,γ-selinene and cinnamic aldehyde,which mainly from Atractylodes macrocephala. Conclusion The chemical constituents in herbal pair are not the simple totaling of single herb,and the mechanism still remains to be studied further. Objective To investigate the changes in main essential constituents in Atractylodes macrocephala and Ramulus cinnamomi and their herbal pair, further provides for for the pairing rules of Traditional Chinese Medicine and unveiling novel bioactive constituents. Methods The Essential constituents were extracted from Atractylodes macrocephala and Ramulus cinnamomi macrocephala and their herbal pair by employing the steam distillation, measured by GC-MS and the overlapped spectral peaks were analyzed by chemometric resolution method (CRM); temperature-programmed retention indices were employed for qualitative analysis. Results Totally 29, 66 and 55 Essential accounting for 95. 93%, 94. 43% and 96. 35% of total essential oils correspondingly. Single herbs and their pairs had four common constituents, accounting for 13 . 14% of total essential oils. After processed in t The main essential constituents in herbal pair were 2- (2-Methoxyphenoxy) phenol, γ-galactopyranoside, which were identified from the herbal pair; 33 constituents were not identified from Ramulus cinnamomi and 7 were not found from Atractylodes macrocephala. selinene and cinnamic aldehyde, which mainly from Atractylodes macrocephala. Conclusion The chemical constituents in herbal pair are not the simple totaling of single herb, and the mechanism still remains to be studied further.