Soybean protein isolate (SPI) was used as raw material for hydrolysis with Alcalase (0~180min).The structural changes of enzymatic hydrolysis products were investigated by gel electrophoresis, Fourier transform infrared spectroscopy (FT-IR) and intrinsic fluorescence spectra. The interfacial behavior of enzymatic hydrolysis products was described by surface tension and adsorption of interfacial protein, and the influence of structural changes and interfacial behavior on the foam properties was analyzed. After enzymatic hydrolysis, the typical 7S and 11S bands disappeared and new bands were produced (about 24ku). Compared with SPI, the content of α-helix was decreased, the content of β-turn and random coil was increased in hydrolysate, and the fluorescence wavelength was red shifted. These results indicated that the protein structure was unfolded, which in turn promoted the change of protein function. The results showed that the foamability of the sample was the best (143.20%) at 90min,which may be due to the lowest average particle size (208.10nm), high solubility (90.44%) and lowest surface tension of the hydrolysate at this time, which was conducive to improving the adsorption rate of the hydrolysate at the air-water interface. However, due to the small peptides produced by enzymolysis, the ability of protein network structure was lost, which had a negative impact on foam stability. In addition, the antioxidant activity of the protein was greatly improved by enzymatic hydrolysis. The foamability of SPI can be effectively improved through enzymatic hydrolysis, and the application range of SPI as an effective foaming agent in food was expanded.