Abstract: To study the changes of volatile compounds and antioxidant activity of organic sulfides in Allium macrostemon Bunge after fermentation. The volatile compounds in Allium macrostemon Bunge and its fermented products were detected by GC-MS, and the antioxidant activities of the main volatile compounds-organic sulfides after separation and purification were compared. The results showed that a total of 39 volatile compounds were detected, which were mainly composed of aldehydes, alcohols, esters, acids and organic sulfides, of which 27 kinds were found in fresh Allium macrostemon Bunge and only 23 kinds in fermented products. After fermentation, 16 kinds of volatile compounds disappeared, including 1-dithiane, propionaldehyde, propenyl methyl sulfide, pentaldehyde, hexanal, dimethyl tetrasulfide, methacryl disulfide, etc.. 12 kinds were added, mainly acetic acid, 2-butanol, 1-malondialdehyde, etc.. 10 kinds of volatile substances decreased, mainly methanol, dimethyl trisulfide, dimethyl disulfide and other sulfides. The organic sulfides in Allium macrostemon Bunge and its fermented products were isolated and purified, and the antioxidant activities of the purified components were studied in four aspects:DPPH free radical scavenging ability, Fe²⁺ chelating ability,·OH scavenging ability and total reducing ability.It was found that the·OH scavenging ability and total reduction ability of the second component of fresh small root garlic separation and purification liquid were strong.However, the DPPH free radical scavenging ability and total reduction ability of the first component of the isolated and purified liquid of fermented small root garlic were stronger.