The　effect　of　welding　heat　input　ranging　from　1.507　KJ/mm　to　2.987KJ/mm　on　low　temperature　toughness　of　deposited　metal　made　by　self-shielded　flux-cored　wire　has　been　investigated.　The　results　showed　that　low　temperature　toughness　decreased　with　the　increase　of　heat　input,　and　the　impact　fracture　changed　from　ductile　to　cleavage　fracture.　In　addition,　the　chemical　compositions　demonstrated　a　slight　tendency　to　decrease　with　increasing　heat　input.　While,　heat　input　has　little　effect　on　inclusions　of　deposited　metal.　Higher　heat　input　lead　to　grains　coarsened　further,　reduced　acicular　ferrite　and　granular　bainite,　and　increased　polygonal　ferrite,　which　mainly　lead　to　toughness　decreased.