The effect of oat β-glucan (OG) on the structure, interfacial behavior and emulsion rheological properties of sea bass myofibrillar protein (MP) was investigated. Fourier transform infrared spectroscopy demonstrated that adding OG decreased the α-helix content in MP from 27% to 22% and increased the β-sheet content, suggesting that OG facilitated MP unfolding. When the OG content was 1.2%, the interfacial tension decreased by approximately 20%, and the diffusion rate increased by approximately 1.5-fold. These changes augmented the physical stability of emulsions. Rheological analysis showed that 3% OG promoted the energy storage modulus (G') of the emulsion. These changes enhanced MP adsorption and rearrangement at the oil-water interface, which enhanced viscoelasticity in the interfacial film and further increased the emulsion stability. These findings augment the understanding of protein-polysaccharide interactions and provide guidance for improving protein emulsion stability.