Abstract : This article mainly discuss the active substance (onion oil) in Allium cepa L. and the relative content of various substances. Taking into account the active material in fresh onion in the content is extremely low, we decide to buy dehydraed onion powder instead. In the meanwhile, some components in onion are heat-sensitive materials, in order not to damage those active substance, we finally determine to adopt the preparation method of supercritical carbon dioxide extraction of onion oil. After analyzed by GC/MS, 65 peaks were separated from the oil.and 19 compounds were identified.Some chemicals were the first time separated from the plant.These compounds identified took up 77.6% of the total areas and 29.2% of all compounds.The results showed that main compounds of Chinese Allium cepa L. were the main 3,5-diethyl-1,2,4-trithiane, 4-hydroxy-4-methyl-2-pentanone, 6-amino-1H-
[1,3,5]triazine-2,4-dione, 3,4-dimethylthiophene and other thianes, thiols, sulfides..
These compounds were partly different from these of the same over sea species which had sulfoethers as main components.
Keywords : Onion;Supercritical fluid;Extraction;GC/MS