Abstract: With Al-SiO₂-sucrose as reactive system, Al₂O₃-Si hollow ceramic microspheres were synthesized using SHS flame quenched technology. Reaction mechanism of hollow ceramic microspheres was studied. The results show that sphere, similar sphere and irregular powders constitute the spraying products. The sphere and similar sphere powders are hollow structure and constitutive of Al₂O₃-Si diphase and maybe a few unreactive SiO₂. The irregular powders are constitutive of SiC、 C and maybe some SiO₂ and reactive but not spherical particles. High reactive heat quantity and fast reaction rate make for the formation of ceramic droplets and the gas produced by carbon is the key factor to form hollow structure. All above three factors determine the formation of hollow ceramic microspheres.