Abstract: In order to improve the functional properties of soybean protein isolate (SPI), grinding was used to physically modify commercial SPI. Furthermore the effects of different grinding time on the structure, properties, and film-forming properties of SPI were investigated. The results showed that the SPI was unfolded after grinding, and the internal hydrophobic groups were exposed, which improved the lipophilicity and foaming properties of SPI. Moreover, grinding could make the SPI film more compact and uniform. The optical properties, physicochemical properties and mechanical properties of the film were also improved after grinding. At 15 min of grinding, the foaming capacity and foam stability of the SPI reached the best (156.21% and 82.33%). Meanwhile, the film performed the least cracks, the most compact structure, the most transparent color (the transparency 0.52), the smallest water vapor permeability (3.33×10^-9 g·m·m^-2·s^-1·Pa), as well as the best tensile strength and elongation at break (2.24 MPa and 178.70%). Therefore, grinding significantly improved the functional properties of SPI. This study may lay a theoretical foundation for widening the application of SPI in food in the future.