Abstract: As an important plant protein with a variety of good processing characteristics, soybean protein isolate (SPI) is widely used in various types of food products, which can improve the quality of food and enhance the quality of food. To enhence the emulsifying properties of SPI, complexes were prepared using SPI and chitosan (CS) as raw materials. The effects of the SPI-CS mass ratio and pH value on the turbidity, average particle size, Zeta potential, and emulsification properties of the SPI-CS complexes were investigate. The results indicated that the SPI-CS complexes prepared at a pH of 5 and an SPI-CS mass ratio of 5∶1 exhibited the highest turbidity; the smallest average particle size, which was (365.0±0.1) nm; the maximum values of emulsification activity and emulsion stability were (15.65±0.15) m²/g and (51.88±0.29)%, respectively. The results of UV spectroscopy and FTIR spectroscopy for SPI-CS complexes showed that changing pH and FTIR spectroscopy were not suitable for the formation of SPI-CS complexes. The UV and FTIR spectra of the SPI-CS complexes showed that changing the pH value and the mass ratio of the two had a great influence on the formation of the SPI and CS complexes, which were mainly formed through electrostatic and hydrogen bonding interactions. The SPI-CS complexes prepared in this study have better emulsification characteristics and can be applied in food emulsion systems.