Using　VC　and　WC-8Co　composite　powder　prepared　by　in-situ　reduction　carbonization　as　raw　materials,　ultrafine　WC-Co　cemented　carbide　was　prepared　by　sinter-HIP　technology.　The　influences　of　the　VC　content　and　the　carbon　content　of　the　composite　powder　on　the　phase　composition,　microstructure,　and　mechanical　properties　of　the　cemented　carbides　were　investigated.　The　results　show　that　the　grain　size,　hardness　and　fracture　toughness　of　cemented　carbides　are　mainly　affected　by　the　VC　content.　These　properties　change　monotonically　with　the　increase　of　VC　content.　The　change　of　transverse　rupture　strength　with　VC　content　is　related　to　carbon　content.　The　compression　strength　decreases　first　and　then　increases　with　the　increase　of　temperature.　With　the　optimized　carbon　content　of　WC-8Co　composite　powder　in　the　range　of　5.60wt%similar　to　5.68wt%　and　the　VC　addition　no　more　than　0.5wt%,　the　ultrafine　cemented　carbides　with　high　comprehensive　performance　were　prepared.　The　highest　value　of　TRS　is　4482　MPa　at　room　temperature,　and　compression　strength　is　4914　MPa　at　600　degrees　C.　Based　on　the　characteristics　of　the　microstructure　and　the　stress　distribution,　simulated　by　the　elastic-plastic　finite　element　model,　the　law　of　performance　change　and　the　mechanism　of　its　performance　were　analyzed.