Replacement　of　Co　with　eta　phase　(e.g.　Co6W6C　and　Co3W3C)　is　proposed　as　an　effective　approach　to　resist　against　corrosion　of　WC-Co　coatings　in　environment　of　molten　zinc.　In　the　present　work,　the　nanocrystalline　WC-eta　powder　was　firstly　synthesized　as　the　coating　material　by　a　novel　method　of　in　situ　reactions　using　metal　oxides　and　carbon　black　as　raw　materials.　The　phase　evolution　in　the　process　of　in　situ　synthesis　was　investigated　by　thermodynamic　calculations　and　experiments.　It　was　found　that　the　initial　WO3,　Co3O4　and　C　transformed　firstly　to　CoWO4,　then　to　W　and　W2C,　and　eventually　to　eta　and　WC.　The　formation　of　n　phase　decreases　the　energy　barrier　for　WC　formation　and　hence　the　synthesis　temperature　for　the　composite　powder.　The　duplex　phase　constitution　of　WC　and　eta　was　obtained　with　optimized　conditions,　and　the　composite　powder　had　a　mean　particle　size　of　about　190　nm　with　inner　grain　size　of　about　50　rim.　The　amount　of　Co　in　the　composite　is　controllable　by　adjusting　the　carbon　addition　to　the　starting　materials.