Ti₂AlNb alloys，as representative TiAl-based alloys designed for long-term use in the temperature range of 650-750 ℃，exhibit promising potential for applications in typical aero-engine components. However，their susceptibility to oxide scale instability，interfacial embrittlement，and degradation of mechanical properties under high-temperature oxidation，molten-salt corrosion，and water-vapor environments constitutes one of the key factors restricting their practical engineering application. The Ti₂AlNb alloy primarily consists of O，B2，and α₂ phases，introducing a high density of grain boundaries and phase interfaces within the alloy，accompanied by pronounced compositional partitioning and electrochemical heterogeneity. As a result，Ti₂AlNb alloys exhibit significant interface sensitivity and non-uniform environmental responses under complex working conditions. This review paper focuses on the significant role of the multiphase microstructure in governing high-temperature oxidation and corrosion behavior and systematically summarizes the research progress on Ti₂AlNb alloys. Particular emphasis is placed on the formation and evolution of complex oxide scales characterized by TiO₂，Al₂O₃，and Nb-related oxides. The dual role of Nb in regulating oxygen diffusion and determining oxide types is clarified，and the effects of selective oxidation among different phases and the associated interfacial stress concentration on the long-term stability of oxide scales are discussed. Considering complex working conditions，this work outlines the coupled corrosion-oxidation behavior of Ti₂AlNb alloys in molten salts containing Cl^－ and SO{}_{\mathrm{4}}^{\mathrm{2}-} as well as in water-vapor atmospheres. It clarifies the localized corrosion sensitivity arising from the electrochemical differences between the B2 and O phases， the destructive effects of corrosive ions such as Cl⁻ and SO{}_{\mathrm{4}}^{\mathrm{2}-} on the continuity and compactness of the oxide scale， and the critical impact of hydrogen ingress-induced intergranular embrittlement in water vapor on application reliability. On this basis，various surface protection technologies developed in relation to the multiphase microstructure and the active diffusion behavior of Nb are introduced. These include aluminizing treatments that construct α-Al₂O₃-dominated selective oxide scales，silicide and Si-rare-earth composite coatings that form SiO₂ barrier layers，and MCrAlY-type metallic coatings with diffusion-barrier designs. The stability of coating/substrate interfaces under complex interdiffusion conditions is also analyzed. From the perspective of engineering applications，key challenges remain in understanding multi-interface coupled oxidation and corrosion mechanisms，establishing reliable long-term environmental stability evaluation methods，optimizing integrated coating-system design，and improving service-life prediction. Future research focuses on multiphase interface regulation and the synergistic design of advanced protection systems.