Abstract: 19 phenolic acids and 7 flavonols with relatively good antioxidant activity were selected for binary combination. Iron ion reduction assay(FRAP)and 1,1-diphenyl-2-picrylhydrazyl(DPPH)radical scavenging were established in vitro to determine the antioxidant activity of 133 phenolic acid-flavanol binary combinations. The relationship between the structure of phenolic acid and flavonol and the antioxidant effect(synergistic,antagonistic and additive)of binary composite systems were studied by differences and difference rates between experimental and theoretical values. The results showed that the structure of phenolic acid and flavonol had significant effects on the antioxidant of binary combination. In the FRAP antioxidant assay,or cinnamic acid phenolic acid with resorcinol structure showed synergistic effect in the binary combination. The methoxyl structure on the B ring of flavonol enhanced the synergistic effect of the binary combination,while flavonol with the steric resistance structure weakened the synergistic effect of the binary combination. The more methoxyl group on overring of phenolic acid,the more significant antioxidant activities of the binary combination would be. In the DPPH antioxidation assay,the synergistic effect of the binary combination with phenolic acid of para-hydroxyl structure was stronger than that of ortho-hydroxyl structure phenolic acid,and the phenolic acid binding steric resistance structure decreased the synergistic effect of binary combination. The results could provide a theoretical basis for choosing the best combination of polyphenols when designing new dietary supplements or fortified foods.