Abstract: By using GC/MS, the process of oxidizing reaction of atractylone is studied, and five decomposition products are obtained, which is greatly different from the references-only two decomposition products, and the mechanism of oxidizing reaction of atractylone is investigated. The hypothesized mechanism of reaction is:atractylone is readily to additively react with water and to generate the semiacetalhydroxyl at 1, 4-site. The loop of it is opened and lead to the cleavage of C-O bond because of the existence of water, the carbonyl is thus formed. The carbonyl is then oxidized to generate carboxylic group. As the carbon atom is sp² hybridization, carboxyl can be attacked by hydroxyl from both sides of hybrid orbital, in this reaction, water is removed, and the remaining atoms are joined to form atractylenolideⅠ and iso-atractylenolideⅠ. While the proton of 7-carbon of atractylenolide Ⅰ is rather active and liable to be replaced by hydroxyl to form atractylenolide Ⅲ and atractylenolide Ⅲ is unstable and dehydrated within molecule to form atractylenolideⅡ. Moreover, atractylenolideⅢ and atractylenolideⅠ are dehydrated between two molecules to generate biatractylolide. By quantitatively analyzing the percentage of pure atractylone and atractylone in herb, the kinetic parameter is obtained, and the equations are:Rate₁=k'₁[x]^1.84, Rate₂=k'₂[x]^1.89, the activation energy of each is 58.05 kJ/mol and 63.17 kJ/mol respectively.