Abstract: To obtain a bifunctional soy protein with antioxidant activity and emulsifying properties, soy protein isolate (SPI) was modified by combining hydrodynamic cavitation with gradient addition of rutin. The changes in physicochemical, structural, and functional properties of SPI before and after modification were analyzed. The results showed that after hydrodynamic cavitation treatment, the surface hydrophobicity of SPI increased, its structure unfolded, and the active groups were exposed, leading to a significant increase in its binding capacity with rutin (P<0.05). As the addition amount of rutin increased, the ultraviolet absorption of SPI enhanced, while the fluorescence intensity decreased with a red shift in the maximum absorption peak. The surface hydrophobicity, free thiol content, and free amino content all decreased. Furthermore, the contents of α-helix, β-sheet, and β-turn in the secondary structure decreased, while the content of random coil increased. Further analysis of antioxidant activity and emulsifying properties revealed that the conjugates formed by combing hydrodynamic cavitation treated SPI with rutin exhibited enhanced antioxidant activity and emulsifying properties. When the addition amount of rutin was 1 mg/mL, in terms of antioxidant activity, the DPPH free radical scavenging capacity increased from 77.80%±0.86% (before modification) to 83.76%±0.65%, the ABTS⁺ radical scavenging capacity increased from 53.09%±0.43% to 63.64%±0.53%, and the ferric reducing power increased from 1.12±0.06 to 1.29±0.12; In terms of emulsifying properties, the emulsification activity index increased from 24.50±1.37 m²/g to 28.55±0.43 m²/g, and the emulsification stability index increased from 69.25±1.77 min to 88.75±1.65 min. Therefore, hydrodynamic cavitation treatment combined with appropriate amount of rutin could effectively improve the functional properties of soy protein, which provided a new approach for protein modification.