Objective To expand the application fields of distillers dried grains with solubles and improve its market value.Methods Arabinoxylan (AX) was extracted from distillers dried grains with solubles and modified to prepare AX with different molecular structures. AX was then reacted with soy protein isolate (SPI) via the Maillard reaction to prepare the AX-SPI covalent complex. The structure of the complex was characterized using circular dichroism spectroscopy, Fourier transform infrared spectroscopy, particle size, and Zeta potential, and its emulsifying properties were studied.Results The AX-SPI covalent complex is formed by SPI and AX via the Maillard reaction, and differences in the polysaccharide molecular structure affect the extent of the Maillard reaction. As the relative molecular mass and chain length of the polysaccharide increase, the difficulty of its attachment to the protein peptide chain also increases. Compared with SPI, the protein solubility of the covalent complex increases by 16.29%, indicating that the solubility of the complex in the isoelectric point region is significantly improved. The average particle size (0.799 μm) of the emulsion stabilized by AX-SPI is small and evenly distributed, and the absolute value of the Zeta potential is high (38.19 mV).Conclusion The AX-SPI covalent complex exhibits better emulsification and stability than SPI. Moreover, the emulsifying properties of the complex increase with the decrease in the relative molecular mass of the polysaccharide. When the relative molecular mass is similar, a shorter polysaccharide chain length results in better emulsifying properties.