With the development of heavy-duty gas turbines， its gas inlet temperature keeps increasing， and the traditional YSZ coatings could not service above 1200 ℃. The LaMgAl₁₁O₁₉（LMA） and YSZ coatings are fabricated byair plasma spray method， and the static oxidation tests are carried out at 1100 ℃ and 1300 ℃. The porosity， microstructure， and phase transformation process are investigated comparatively by SEM and XRD. The results show that the porosity of LMA coatings increases with the sintering time increasing at 1100 ℃ and 1300 ℃， while the porosity of YSZ coatings decreases obviously. The amorphous phase of LMA coatings is transformed rapidly at high temperatures. The needle-like grain at LMA coating fracture is formed， and the grain growth becomes platelet-shaped grains with the sintering time increasing， which improves the sintering resistance of LMA coatings. The results of YSZ coatings Rietveld refinement show that the content of the T′ phase decreases from 82.67% to 27.69% with the sintering time increasing to 1000 h at 1300 ℃. Meanwhile， the content of the C phase rises from 1.50% to 46.84%， and the M phase increases from 0.19% to 15.39%. This phase transformation causes volume transformation， which generates large residual stress，leading to the coating falling off.