Abstract: The catechin is one kind of polyphenol. It is made up of four isomers. Its’ molecular orbital was designed accordingto Hückel molecular graph theory and the wave function and characteristic values were obtained by using molecular orbitalperturbacion theory. Based on the date the thermodynamic equilibrium constant was resulted.

Key words: Hückel molecular orbital, molecular orbital perturbaciow theory, wave function, characteristic value, thermodynamic equilibrium constant