Heterogeneous precipitation method was used to prepared surface coating on self-made BaMgAl10O17 : Eu phosphor. Results illustrate that the coating film can be silicon dioxide in amorphous state with 50 nm in thickness. Photolumi-nescence results indicate that the coating layer presents an observable improved effect on the enhancement of thermal stability. When baked at 600℃for 1 h, the luminance of coated BAM keeps at 92% higher than that of uncoated BAM by 23% . This protective effect can be attributed to the high compact degree and uniformity of this amorphous SiO2 coating film which is served as a diffusion block layer to inbreak oxygen atom, thus releases the oxidation extent of Eu2 + effectively. Heterogeneous precipitation method was used to prepare surface coating on self-made BaMgAl10O17: Eu phosphor. The results show that the coating film can be silicon dioxide in amorphous state with 50 nm in thickness. Photoluminescent-nescence results indicate that the coating layer presents an observable effect on the enhancement of thermal stability. When baked at 600 ° C for 1 h, the luminance of coated BAM keeps at 92% higher than that of uncoated BAM by 23%. This protective effect can be attributed to the high compact degree and uniformity of this amorphous SiO2 coating film which is served as a diffusion block layer to inbreak oxygen atom, thus releases the oxidation extent of Eu2 + effectively.