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 degrees C for reaction Mg+3B(2)O(3)+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.