Different　from　Neuber＇s　rule　or　Glinka＇s　energy　method　which　are　always　adopted　to　characterize　the　notch　tip　field　under　elastoplastic　condition,　in　this　paper,　the　strain　energy　rate　density　(SERD)　rule　is　used　for　viscoplastic　materials.　In　particular,　based　on　the　definition　of　generalized　notch　stress　intensity　factor　(G-NSIF)　for　sharp　V-notch　in　viscoplastic　solids,　the　concept　of　SERD　for　sharp　V-notch　in　viscoplastic　solids　is　presented.　Subsequently,　by　taking　as　a　starting　point　the　SERD,　the　averaged　strain　energy　density　(SED)　for　sharp　V-notch　in　viscoplastic　solids　is　derived　with　integration　of　time.　The　fracture　toughness　relation　between　sharp　V-notch　specimens　and　crack　specimen　in　viscoplastic　materials　is　given　based　on　the　transformation　of　SERD.　A　numerical　approach　is　presented　to　compute　the　SERD　and　SED　based　on　finite　element　method.　Some　crucial　comments　on　the　G-NSIF　have　been　discussed.　Some　typical　solutions　for　SERD　and　SED　for　sharp　V-notched　specimens　are　investigated.