Abstract: The optimized conditions of ultrasound-assisted enzyme modification and the effects of modification on the emulsification properties of Chlorella protein were investigated in this paper. The ultrasonic time, ultrasonic power, enzyme addition and enzyme reaction time were selected as the investigating factors. The analytic hierarchy process (AHP) was used to weight the emulsification activity, emulsification stability and creaming index, and the comprehensive weighted score was used as the response value. A four-factor, three-level response surface method was used to investigate the optimal modification conditions for the emulsification properties of ultrasound-assisted enzyme-modified Chlorella protein. The results showed that the optimal modification conditions were as follows: Ultrasonic time 31 min, ultrasonic power 209 W, enzyme addition 3.1% and enzyme reaction time 3 h. Under the optimized conditions, the best score of emulsification performance was 98.99, which was close to the predicted value. Compared with the original protein, the solubility and foaming ability of modified Chlorella protein increased by 68.30% and 49.44%, respectively. However, the modification of water-holding and oil-holding properties showed no significant effect. In summary, this study could provide certain theoretical basis for the application of Chlorella protein in food emulsification systems.