Ternary Al-Mg-Zr alloy fuels with Mg content ranging from 5% to 30% were prepared by a close-coupled gas atomization. The phase composition, morphology and exothermic oxidation behavior of the alloy powders were characterized by X-ray diffraction, scanning electron microscope(SEM)/ energy dispersive spectrometer (EDS) and thermogravimetry-differential thermal analysis (TG-DTA) respectively and an oxidation reaction mechanism model was proposed to explain the intensive oxidation exothermic phenomenon. Results show that the alloy powders consist of Al, Al₃Mg₂, Al₃Zr and Al₁₂Mg₁₇ mainly, and the powder has good sphericity. With the increasing of Mg content, the oxidation reaction temperature of Al-Mg-Zr alloys decreases, the multi-step oxidation process gradually transforms into single step oxidation process and the energy releasing amount increases first and then decreases. The intensive exothermic oxidations of Al₇₈Mg₂₀Zr₂ and Al₇₃Mg₂₅Zr₂ powders occur at 945 ℃ and 938 ℃, respectively. The intensive oxidation reaction of Al₇₈Mg₂₀Zr₂ powder is relatively complete and the highest exothermic enthalpy of oxidation of the powder is 9798.8 μV·s·mg^-1.