CaB₆ powder was prepared by combustion synthesis with CaO, B₂O₃ and Mg as reactants. The DTA curves of the different reaction systems were investigated. Combustion products and leached products were characterized by XRD, SEM and particle size distribution techniques. The results indicate that apparent activation energy(E) of the exothermic peak near 872℃ for reaction Mg+3B₂O₃+CaO=CaB₆+10MgO is 15.71kJ·mol^-1 and its reaction order(n) is 1.1. The apparent activation energy is lower, so the reaction occurs easily. Combustion products consist of MgO, CaB₆ and a little amount of Mg₃B₂O₆ and Ca₃B₂O₆, and no nitrides form during the combustion process in air. CaB₆ powder purity is 92.5% after combustion products are leached with
acid. CaB₆ particles become finer with the increasing of the preparing sample pressure.