Abstract: This article studies the effect of SiO₂ to be coated on the surface of alloy Al-Mg-Si on its directed oxidation at hight emperature in air. The experiment observed the morphology of the surface of alloy Al-Mg -Si formed by directed oxidation. It was discovered that SiO₂ can make the oxidation growth of Al₂O₃/Al composite in the way of gloss not of cell-shape, which raised the relative density of the material. In addition, it was f ound that SiO₂ could decrease the incubation period needed for the directed oxidation of Al-Mg-Si alloy and reduce the growth time of Al₂O₃/Al composites