In this article, we demonstrate that the Al-alloyed Ag nanoparticle-embedded alumina nanocermet films lead to excellent thermal stability, even at 500 °C for 130 h under an ambient nitrogen atmosphere. The outward diffusion of Al atoms from the AgAl bimetallic alloy nanoparticles and their easy oxidation create an armor layer to suppress the mobility of Ag atoms. Then, the AlAg particles or/and agglomerates with a uniform spherical shape favor higher dispersion concentration within the host matrix, which is beneficial both for high absorptance in the visible range and for the solid localized surface plasmon absorption features in the AgAl-Al2O3 nanocermet films. Based on the AgAl-Al2O3 absorbing layer with sound optical and microstructural stability, we successfully constructed a high-temperature-endurable solar selective absorber. The multilayer stacked absorber demonstrates a high solar absorptance of ∼94.2% and a low thermal emittance of ∼15% (@ 673 K) after annealing at 450 °C for 70 h in an ambient nitrogen atmosphere.