With increasing awareness of health and sustainable dietary pattern, plant-based proteins have shown a growing interest as substitutes for animal proteins. Meanwhile, the non-covalent interaction of protein with natural phenolic compounds can be used to develop functional ingredients. In this work, Alcalase hydrolysates of soy protein isolate (HSPI) were used to fabricate complexes with tannic acid (TA), and their physicochemical properties were investigated and compared with soy protein isolate (SPI) and sodium caseinate (SC) to get insights into the advantage of polyphenol modification. The complex solution showed reduced particle size, higher turbidity, and higher surface charge with increasing TA concentration. The interaction mainly occurred through hydrogen bond and hydrophobic interaction, leading to the unfolding of protein molecular structure. The complexes displayed lower interfacial adsorption activity and reduced interfacial viscoelastic modulus upon increasing TA concentration possibly because of the interference of TA on the diffusion and molecule interaction of protein hydrolysates to form elastic films. Nonetheless, the complex-based emulsion showed enhanced emulsifying stability with small droplet size, superior oxidation stability, high physical stability against heat and freeze-thaw treatment due to the higher surface charge and formation of particle-stabilized interfacial membrane. These findings provide insights for developing plant-based protein with excellent emulsifying properties, which show great potential for application as SC substitute in dairy-free emulsified products.