Abstract: To clarify the effect of lipid peroxyl radicals on the structure and processing properties of egg yolk protein, peroxyl radicals produced at different concentrations of 2,2'-Azobis (2-methylpropylimide) dihydrochloride (AAPH) was applied to egg yolk proteins under aerobic conditions to study the changes of structure, physicochemical properties and functional properties of egg yolk protein. The results showed that the carbonyl content of egg yolk protein was significantly increased (P<0.05) and the total number of sulfhydryl groups was significantly reduced (P<0.05) with increasing AAPH concentration. Meanwhile, the secondary and tertiary structure of egg yolk protein changed obviously, and protein aggregation occurred with the intensification of oxidation reaction. The surface hydrophobicity showed apparent increased and then decreased. The absolute value of zeta potential showed a tendency to decrease firstly and then increasibng, and finally decreasing. In addition, the continuous oxidation resulted in the decrease of solubility of yolk protein, and the emulsification performance analysis indicated that 0.5 mmol/L of AAPH could achieve the best emulsification performance of yolk protein. Principal component analysis (PCA) showed that the effects of peroxy radical produced under different oxidation degrees on egg yolk protein varied obviously. This study revealed the changes of egg yolk protein under AAPH oxidation system, which would provide a certain reference basis for the oxidation control and quality control in egg processing.