In order to investigate the combustion characteristics of Al powders in NOx， the reaction mechanism of Al with three nitrogen oxides （NO₂， NO and N₂O） was studied by means of density functional theory ωB97X. Firstly， the geometries of reactants， intermediates， transition states and products were optimized with all parameters. The authenticity of intermediates and transition states was confirmed by frequency analysis. The transition states were further determined by intrinsic reaction coordinates （IRC） calculation， and then the detailed reaction paths and mechanisms were obtained. High precision single-point energy of each structure was obtained by using the double hybrid functional PWPB95 combined with DFT-D3 correction and def2-TZVPP basis set. The rate constants of the related reactions were calculated by using the variational interpolation transition state theory， and the Arrhenius expressions for each reaction are obtained. The results show that the reaction process of Al with NO and NO₂ is that Al and O atoms join together to form the intermediate of the complex， and then break the N─O bond through the ternary ring transition state to form the product. When Al reacts with N₂O， Al reacts with N atoms to form a complex and then the elimination reaction takes place through the ring transition states. The activation energies of the reaction of Al with NO₂， NO and N₂O are 4.3 kJ·mol^-1，249 kJ·mol^-1 and 13.4 kJ·mol^-1， respectively. From 2400 K to 4100 K， the reaction rate of Al with NO₂ and N₂O is higher than 106 m³·mol^-1·s^-1， which indicates that the reaction is easy to take place and the reaction rate is very fast， and the reaction rate of Al with NO is about 1/10000 of that of Al with NO₂ and N₂O.