This　paper　focused　on　toughening　mechanism　of　weld　metal　for　self-shielded　flux-cored　wire　after　a　review　of　development　history　of　self-shielded　flux-cored　wire.　Toughness　impact　of　inclusion　depended　on　its　shape　and　sizes.　Circular　inclusion　ranging　from　0.2　to　1.0μm　has　a　tendency　to　form　AF　core　and　is　favorable　for　toughness　improvement.　To　maintain　the　relatively　higher　toughness,　optimum　ratio　of　aluminum　to　oxygen　in　weld　metal　is　0.84.　The　additions　of　trace　element　such　as　Li,　Zr,　Ti,　B,　Ni　and　Ce　in　flux-cored　wire　help　to　improve　weld　impact　toughness.　In　addition,　droplet　transfer　modes　and　formation　mechanism　of　spatter　was　also　summarized.