As　steel　strength　increases,　the　fracture　toughness　may　be　quite　different　from　that　of　normal　steel,　and　the　corresponding　welded　joints　can　be　the　critical　spots　due　to　possible　brittle　fracture　behavior.　Moreover,　the　design　load　for　high-strength　steel　structure　is　larger　and　the　steel　with　higher　stress　is　more　sensitive　to　defect,　which　increases　the　potentials　of　brittle　fracture.　The　service　of　steel　structures　in　cold　regions　increases　the　crisis　of　brittle　fracture.　Therefore,　a　series　of　three-point　bending　tests　were　conducted　at　low　temperature　to　investigate　the　fracture　toughness　of　high-strength　steel　and　its　butt　weld.　Fracture　micro-mechanisms　were　analyzed　through　Scanning　Electron　Microscopy　of　the　fractured　surfaces　in　specimens.　The　fracture　toughness　indices　(critical　CTOD　values)　of　high-strength　steel　and　its　butt　weld　all　decrease　as　temperature　decreases.　The　heat　affected　zone　(HAZ)　is　more　critical　to　fracture　than　the　base　material,　indicated　by　much　lower　critical　CTOD　values　and　higher　transition　temperature.　The　fracture　toughness　of　high-strength　steel　is　relatively　lower　than　the　conventional　steels　(i.e.　235MPa,　345MPa　and　390MPa).　The　results　obtained　in　this　paper　provide　reference　for　the　fracture　resistant　design　of　high-strength　steel　structures　in　cold　regions.