Aluminum nitride (AlN) powder was heated at 500~700 ℃ in protective gas mixed with high nitrogen and low oxygen,in order to investigate the effect of heat treatment on AlN powder's surface properties and hydration resistance.The results show that the surface of AlN powder was coated by a structure of oxidation product,which is favor to form a diffusion barrier between water and AlN surface,thus restrain hydrolysis reaction and increases the water-resistance of AlN powder in wet environment.After heat treatment,the AlN powder kept high stability of hydration resistance in aqueous ball milling at a high cutting stress.