The binding degree of soy protein isolate (SPI) to dextrans (D) was changed by increasing the concentration of polyethylene glycol (PEG) by using PEG to bind the SPI and D through Maillard in a crowded liquid system. By increasing the concentration of PEG to change the degree of solute crowding in the solution, the effects of crowding at different degrees on the SPI-D Maillard response were investigated, and the changes in the structure of the SPI-D complexes were studied. Macromolecular crowding effect as a new concept in life science was introduced to the present study. In recent years scientists strongly suggested that much like pH value, ionic strength, or solution composition, the degree of molecular crowding should be considered as an important factor for describing the environmental conditions in a solution. The free amino group content and sodium dodecyl sulfatepolyacrylamide gel electrophoresis (SDS-PAGE) were used to study the binding of SPI-D complex under different PEG concentrations. The infrared spectrum was used to indicate the hydrophobicity, free sulfhydryl content and turbidity analysis. And structureactivity relationship analysis of different saccharification degrees structural changes and functional properties of the expression of SPI emulsifying properties. The results showed that with the increase of PEG concentration, the degree of complexation of the complexes was increased, the structure of the protein was changed, the structure of αhelix was decreased, the irregular curl was increased, the hydrophobicity was decreased, and the emulsification performance continued to be improved. When the PEG concentration was 0.06g/mL or more, the saccharification growth rate of the SPI-D complex was slowed down. 