Objective: To discuss the influence of drug compatibility on the components of the volatile oil in Menthae Haplocalycis Herba and Schizonepetae Spica

and to provide a basis for researching basis of effective material for the drug pair. Method: Steam distillation was used to extraction of the volatile oil Menthae Haplocalycis Herba

Schizonepetae Spica and their combination. GC-MS was used to analyze the volatile oil of them. Result: 40 compounds were identified from the volatile oil of Menthae Haplocalycis Herba

including 21 compounds were not detected from the drug pair oil;27 compounds were identified from the volatile oil of Schizonepetae Spica

including 6 compounds were not detected from the drug pair oil. In volatile oil of the drug pair

there are 35 compounds were identified

including 5 new components that were not detected in volatile oil of single Medicinal herbs. Conclusion: There were some changes between the volatile oil of single Medicinal herbs and the volatile oil of the drug pair.These phenomena may be due to the occurrence of certain chemical reactions and physical changes in compatibility of decocting process. Further research is worth change compound group and the corresponding compatibility after decocting efficacy.