Aluminum nitride (AlN) was synthesized by direct combustion of spherical Mg-Al alloy powder in air. The alloy (Al₁₂Mg₁₇) heaped up within a heating area (1 cm in diameter) and was ignited by butane flame. Synthetic process was recorded by a high-speed camera. Morphology and phase makeup of initial powder and combustion products were analyzed by scanning electron microscope and X-ray diffraction. Thermodynamic property of the alloy was analyzed using TG-DSC. The results show that the Al in the Mg-Al alloy powder can be completely transformed to AlN. Ignition temperature of the alloy is about 494.4℃. Once the alloy powder is ignited, self-sustained combustion in the powder can be observed. When combustion begins, Mg can rapidly vaporize and react with oxygen. This oxidation reaction can consume the oxygen around the particles, leading N₂ diffusing to the liquid Al layer. Combustion products of the alloy consist of two different layers.The upper white layer contains only MgO and the lower black layer contains only AlN. During synthetic process, the existence of Mg significantly promotes the nitridation of Al.