Abstract: To study the antioxidant ability order of the four flavonoids compounds from  Medicago sativa  L. Four main flavonoids from the Medicago sativa  L. were studied using the Density Functional Theory (DFT) B3LYP method with 6-311 + + G (d,p) basis set.Their activities were analyzed based on molecular structure,free radical geometry,bond dissociation energy (BDE) and the energy gap between HOMO and LUMO.The antioxidant ability order of the four flavonoid compounds is Quercetin＞Luteolin＞Genistein＞Formononetin,which is consistent with the experimental conclusion reported in literature.The results showed that the DFT method can provide theoretical guidance for the selection of natural flavonoid antioxidants.

Key words: Medicago sativa L., flavonoid, DFT, bond dissociation energy (BDE), antioxidant activity