The thermodynamic calculation and analysis of combustion synthesis reaction of Al - Cr₂O₃ system with AI₂O₃ and Cr₂O₃ diluents were conducted, and the effects of reaction starting temperature T_O, diluents AI₂O₃ and Cr₂O₃ on the adiabatic combustion temperature T_ad were also discussed. The near linear relation between T₀ and T_ad was obtained and its application in directing the composition design was introduced. Furthermore, the correlation between Gibbs free energy AG and reaction temperature T was displayed by above calculation and discussion. It shows the reaction of this system is controlled by diffusion. At last, combined with the analysis on the experiment results, the thermal explosive reaction micro-model was proposed.