In this study, the ABTS free radicals scavenging activity was as an indicator, the Chou-Talalay method was used to investigate the synergistic antioxidant effect and structure activity relationship of six kinds of small molecules with different structures. The results showed that the ABTS free radicals scavenging activity of the six kinds of flavonoids was in following order, i.e., 5,6,7-trihydroxy flavone > 6-hydroxyl flavone > 3,7-dihydroxy flavone > 5-hydroxy flavone > 3-hydroxy flavone > 7-hydroxyl flavone > ascorbic acid. Among them, 5,6,7-trihydroxy flavone, 6-hydroxy flavone and 3,7-dihydroxy flavone oxidation effect significantly, under different concentration and two flavonoid compounds on ABTS free radicals scavenging activity of the combined effect of CI values are quite different, dihydroxy flavone and other five kinds of flavonoids have obvious synergistic effect. It was also found that the synergistic antioxidant effects of the six flavonoid compounds were related to the position and quantity of the hydroxyl group, the main structural feature of the synergistic antioxidant effect of 3,7-dihydroxy.