Abstract: In present paper, the principal volatilc constituents of Chinese medicinal herbs, Curcuma longa L., A.lancea(Thunb.)DC.,Foeniculum vulgare Mill.And cinna-momun cassia presl have been analyzed by means of flash distillation/capillary gas chromatography/mass spectrometry.The results obtained were similar to that of conventional steam distillation-extration method.But this new technique possesses such advantages: rapidity, simple manipulation, micro quantity of plant sample used and the exclusion of interference from impurities in the extrating solvents.It proves to be a promising tool for analysis of volatile constituents of natural products.The optimum condition of flash distillation has also been studied.