In this paper, the correlations between the cleavage degree of disulfide bonds and soy protein surface activity had been studied in order to show the surface activity of soy protein. The disulfide bonds of soy protein were oxidized to sulfonic groups by performic acid. The distribution of polar and nonpolar groups, and the molecular structure of soy protein were changed because of the oxidation damage of disulfide bonds, and these changes led to changes in surface activity of soy protein. The results showed that the emulsifying property of soy protein was improved by oxidizing the disulfide bonds of protein compared with that of natural soy protein. The change of soy protein emulsifying property is closely related with the degree of the disulfide bond oxidation damage,and that was also an effective way to prepare the protein-based surfactant.