The calculations based on the density functional theory (DFT) have been used to study the structure-activity of resveratrol in the chain reaction of autooxidation. According to the geometry obtained by using a B3LYP/6-31G**, the HOMO, LUMO of resveratrol and the spin density, the single electron distribution of the 4'- and 5-radical of resveratrol were calculated, it was found that resveratrol is a potential antioxidant. The 4'-hydroxyl group of resveratrol is more reactive than 3- and 5-positions because of the resonance effects. The dominant structure of the resveratrol radicals is a semiquinone structure which determines the stability of radicals, and the unpaired electron is mainly distributed to the O-atom and its ortho and para positions. The antioxidant activity of resveratrol is related to the spin density and the unpaired electron distribution of the O-atom.