Green onion is a perennial herb with a characteristic allium aroma. Fried green onion oil has a rich flavor that is popular in traditional Chinese cuisine. Thus, the critical aroma components of fried green onion oil were focused on. The oil samples had a low score of a green aroma but a high score of salty, greasy aromas. Whereafter, a total of 36 aroma-active substances with flavor dilution (FD) factors ranging from 1 to 6561 were identified in fried green onion oil. At the same time, 42 were detected in fried green onion residue with FD factors ranging from 1 to 19683. The omission tests revealed that furaneol, dimethyl trisulfide, allyl methyl trisulfide, (E,E)-2,4-decadienal, etc., were the key aroma compounds in fried green onion oil. In addition, the observation of the reaction of thioethers at high temperatures revealed that dimethyl disulfide undergoes polymerization to form dimethyl trisulfide.