Abstract: The structural and physicochemical properties of protein particles are typically modulated by pH through alterations in surface charge distribution and secondary structural conformations, consequently influencing the interfacial adsorption capacity and stability of Pickering emulsions stabilized by these protein-based emulsifiers via pH-dependent interfacial adsorption mechanisms. The structural and functional characteristics of oat protein isolate (OPI) were systematically investigated across varying pH conditions (3, 5, 7, 9, and 11), with emphasis on microstructural properties, Zeta potential dynamics, and protein subunit compositions. Concurrently, the emulsification performance, oxidative stability, and in vitro digestibility profiles of Pickering emulsions stabilized by OPI were comprehensively evaluated under fixed oil-water phase ratio of 3:7. The particle size of oat protein isolate (OPI) was observed to initially increase followed by a gradual decrease as the pH of the suspension was elevated, with a minimum diameter of approximately 0.27 μm recorded under alkaline conditions. Concurrently, both solubility and absolute zeta potential demonstrated parabolic profiles, with solubility peaking at 12.96% and surface charge reaching maximal electronegativity (−38.01 mV) under alkaline conditions, correlating with structural rearrangements observed in particle aggregation-disaggregation dynamics. The colloidal stability of oat protein isolate (OPI) was critically compromised at pH5.0 under near-isoelectric conditions, resulting in immediate emulsion phase separation within 30 minutes of preparation. In parallel experimental systems where pH was systemically modulated to 3, 9, or 11, significant improvements were quantified including reduced emulsion particle dimensions, enhanced emulsifying activity indices, improved rheological properties, and distinct fibrous network formations characterized by scanning electron microscopy. The pH-dependent stabilization mechanisms of oat protein isolate (OPI)-based Pickering emulsions were systematically elucidated. Specifically, at pH11, emulsion droplet size was minimized to 0.93 μm through electrostatic repulsion effects, while Zeta potential registered a peak electronegativity of −62.69 mV, correlating with enhanced colloidal stability. Concurrently, emulsifying activity index (EAI) was quantified at 38.70 m²/g under alkaline conditions. Lipid oxidation kinetics were significantly decelerated, emulsion stability was augmented through steric hindrance mechanisms, and free fatty acid release rate was elevated to 70.27% during in vitro digestion simulations. These findings validated that structurally stable Pickering emulsions could be successfully fabricated using OPI emulsifiers at pH 3, 9, and 11 via pH-modulated interfacial engineering. This investigation was projected to expand the functional applications of plant-derived proteins in emulsion-based delivery systems, while mechanistic insights into OPI's structure-function relationships were established as theoretical guidelines for designing bio-stabilized colloidal matrices.