The structural characteristics and thermal protection mechanism of a certain type of auxiliary power unit (APU) turbine guide vane in service were analyzed by scanning electron microscope (SEM) and energy dispersive analyzer (EDS). Then, the thickness variation and failure mode of the high temperature protective coating after removal from aircraft were investigated. The results show that there are two different coating structures in the aircraft APU guide vanes: aluminized coating+MCrAlY coating and mono aluminized coating. The MCrAlY coating thickness of the scrapped APU guide vane components increases first and then decreases from the area of trailing edge to the pressure side and then to the leading edge. Affected by the configuration and the service environment of APU guide vanes, the coatings at the trailing edge and pressure side present an oxidation-predominant damage mode. The oxidation degree of the coating on the trailing edge is more serious, while the closer the pressure-side region to the leading edge, the less severe the oxidative damage. However, due to the coupling effect of CMAS (CaO, MgO, Al₂O₃, SiO₂) corrosion and high temperature oxidation, the damage to the coating at the leading edge of vanes is the most serious.