Focusing on the effect of interaction with Epigallocatechin gallate (EGCG) on the structure and function of denatured soybean protein isolate (SPI). Fourier transforms infrared (FT-IR) spectroscopy and fluorescence spectroscopy were used to analyze the structure and conformation of the SPI-EGCG conjugates. The relationship between structural change and functional properties was analyzed through the determination of turbidity, emulsifying ability, emulsifying stability, particle size analysis, and Zeta potential analysis. The results showed that the absolute value of Zeta potential, turbidity as well as emulsifying activity and emulsion stability of denatured soybean protein were increased significantly, whereas its particle size was decreased. After complexation with EGCG, the functional properties of the protein were further improved. The secondary structure of SPI was changed and the protein was unfolded after EGCG were linked to it, which decreased the content of α-helix and increased the content of a random coil. Ultrasound combined alkali treatment also changed the structure of the protein. And the microenvironment around the aromatic amino acid residues in the protein was also changed, resulting in its conformational change. In addition, the fluorescence spectra showed that the fluorescence quenching of ultrasonic-assisted alkali treatment soybean protein by EGCG was a static quenching process with the formation of binding sites close to 1.