More and more attention has been paid to the doubleprotein food, which is beneficial to human health by mixing animal and plant proteins. Therefore, it is vital to understand the structure and properties of soybean-whey mixed protein, and its impact on mixed food texture and sensory quality. The effects of ultrasound treatment on the emulsifying activity and structural properties of soybean-whey (SPI-WPI) mixed protein were studied. The effect of ultrasound treated time on the structural and emulsifying property of SPI-WPI was studied by SDS-PAGE, Fourier infrared spectrum, UV absorption spectra and ANS fluorescence probe emission spectra. The results showed that ultrasound treatment had no significant influence on primary structure of SPI-WPI mixed protein. However, it had a significant effect on secondary structure and tertiary structure. The content of αhelix and βsheet were decreased, the content of βturn was increased, and the content of unordered was also increased slightly with the increase of ultrasound treatment. The results of surface hydrophobicity and UVvisible spectrum showed that the conformation of the mixed protein system was changed because of ultrasound, the polypeptide chains were partially expanded, hydrophobic groups were exposed, and the protein structure became more stretched. The turbidity of the treated samples was significantly lower than that of the untreated samples, indicated that the ultrasound treatment produced a cavitation effect that made the protein molecules more dispersed, and the resulting protein had a higher emulsification activity. The emulsification activity and emulsion stability of the mixed protein system were increased first and then decreased, reaching a maximum at 30min. The results showed that the emulsification of SPI-WPI mixed system could be significantly improved by different treated time.