Freeze　drying　method　for　preparation　of　coating　powders　is　put　forward,　which　doesn＇t　need　a　core　particle　at　first　compared　with　the　conventional　methods.　Nano-sized　Al2O3　coated　W　composites　were　prepared　via　freeze-drying　and　multi-reducing　of　the　mixture　of　aluminum　sulphate　and　AMT.　The　phase　compositions,　structure　and　morphologies　of　the　composites　were　investigated　by　XRD,　IR,　SEM.　The　formation　mechanism　of　the　coating　composites　was　also　studied.　The　results　indicate　that　W　powders　in　size　of　1　μm　have　regular　shape　and　are　coated　with　uniform　Al2O3　nanoparticles　in　size　of　40　nm.　The　mechanism　is　suggested　to　be　three-step　process:　W　crystallization,　soft-coating　formation　and　heterogenous　alumina　nucleation.