Abstract: Supercritical carbon dioxide extraction is a method of decaffeinating tea.But at the same time,it also takes off some aroma substances in tea.By measuring aroma substances in the green tea sample,the decaffeinated green tea sample and extracts in the process with SDE aroma extraction method and GC- MS analysis method,it concluded that the aroma content of the green tea sample was 21.44 μg / g,its main aroma substances were 2,4- Heptadienal,( E,E)-,3- Buten-2- one,4-( 2,6,6- trimethyl-1- cyclohexen-1- yl)-,1,6,10-Dodecatrien-3- ol,3,7,11- trimethyl-,Hexanal,.alpha.- Iononethe,2- Hexenal,( E)-,1,6- Octadien- 3- ol,3,7-dimethyl-,et al.The aroma content of the decaffeinde green tea sample was 9.27 μg / g,its main aroma substances was 2,4- Heptadienal,( E,E)-,1,6- Octadien- 3- ol,3,7- dimethyl-,Hexanal,Benzene,1,3- dimethyl-,2-Hexenal,( E)-,3- Buten-2- one,4-( 2,6,6- trimethyl-1- cyclohexen-1- yl)-,et al.The aroma content of extracts was 31.80 μg / g,its main aroma substances was 2,4- Heptadienal,( E,E)-,2( 4H)- Benzofuranone,5,6,7,7a-tetrahydro-4,4,7a- trimethyl-,3- Buten- 2- one,4-( 2,6,6- trimethyl- 1- cyclohexen- 1- yl)-,Pentanoic acid,Benzaldehyde,et al.The loss rate was 56.76%,and The loss of Benzaldehyde,5- Hepten- 2- one,6- methyl-,2-Octenal,( E)-,Geraniol and 2,4- Decadienal,( E,E)- is serious.In the process of extracting caffeine with supercritical carbon dioxide from tea,the loss of aroma substances was serious.