Objective Composite coating treatment was conducted for strontium aluminate, in order to improve the hydrolytic resistance of fluorescent powder. Methods Liquid hydrolysis method was used to coat the surface of strontium aluminate with SiO₂/Al₂O₃ film, which was then analyzed for water resistance, luminescence performance and morphology. The impact of the coating amount on the encapsulation effect was studied. Results The coating amount showed very important impact on the encapsulation effect. When the film layer was too thin,the water-resistance of the fluorescent powder was limited; when the film layer was too thick,the luminescence of the fluorescent powder was limited. Conclusion Good samples could be obtained if the mass ratio of SiO₂and Al₂O₃ in strontium aluminate could be controlled at around 5% .