Gonggan (Citrus sinensis Osb. 'Deqing Gonggan') is a natural hybrid citrus from Guangdong province. To understand conflicting relationships between the change of flavor quality and total soluble solids and titratable acid contents of Gonggan fruits and study the method of flavor quality keeping at room temperature, we investigated that the flavor quality keeping role of aloin and its effects on soluble sugars contents, and acid invertase activity of Gonggan fruits. The results in this paper show that the change of flavor quality can be evaluated through soluble sugars (sucrose, glucose, fructose) contents, and also not through total soluble solids and titratable acid contents. Aloin reduced the changes of the inclusion contents of Gonggan fruits during storage, extended the flavor quality period from 7 to 15 days, changed the variation patterns of total soluble solids, soluble sugars(sucrose, glucose, fructose) contents and acid invertase activity from s-type of control into half-s-shaped. Its role in flavor quality keeping effect on fructose content change of Gonggan fruits is discussed.