The　P11　heat　resistant　steel　was　welded　by　the　narrow　gap　automatic　TIG　method,　and　the　bead　was　filled　using　multi-layer　single　pass　technology.　Then　the　metallographic　structures　were　observed　and　mechanical　properties　were　tested,　and　the　relationship　between　microstructure　distribution　characteristic　and　micro-hardness　was　particular　searched.　The　results　show　that　the　filling　bead　consists　of　ferrite　and　troostite,　and　the　coarse　and　fine　grained　regions　are　appeared　alternately.　When　compared　with　base　metal,　the　microstructure　is　finer　and　micro-hardness　is　higher.　The　cosmetic　bead　is　mainly　composed　of　coarse　lath　martensite　and　granular　bainite　while　reticular　troostite　emerged,　and　the　micro-hardness　is　higher　than　that　of　filling　bead.　In　heat　affected　zone　(HAZ)　of　filling　bead,　ferrite　and　pearlite　with　a　banding　distribution　are　observed,　which　is　similar　with　the　filling　bead.　In　the　thickness　direction,　the　ultimate　tensile　strengths　of　top　and　bottom　are　almost　the　same,　which　is　corresponding　with　microstructure　distribution　characteristic.　And　the　impact　tests　show　that　absorption　energy　can　meet　all　the　requirements.　©　2016,　Editorial　Board　of　Atomic　Energy　Science　and　Technology.　All　right　reserved.