The　focus　of　this　research　is　the　low　activation　ferrite/martensitic　steel　that　is　used　for　manufacturing　nuclear　fusion　reactor　experimental　blanket　modules.　A　fiber　laser　was　used　to　weld　on　one　side,　realizing　double-sided　forming,　and　the　organization　and　properties　of　the　as-welded　metal　were　systematically　studied.　The　Ta　mass　fraction　varied　in　the　order　of　0%,　0.26%,　0.54%,　and　0.81%.　The　results　showed　that　the　weld　seam　had　been　well　formed　and　did　not　have　other　welding　metallurgical　defects.　With　an　increase　in　the　Ta　mass　fraction　in　the　weld,　the　number　and　size　of　lath　martensite　and　8-Fe　in　the　weld　gradually　decreased;　at　the　same　time,　the　number　and　size　of　ferrite　and　pearlite　gradually　increased.　When　the　mass　fraction　of　Ta　increased　from　0%　to　0.26%,　the　impact　toughness　of　the　weld　increased　from　about　40　J　to　about　82.3　J,　which　is　equivalent　to　an　increase　of　about　2.06　times.　This　increase　is　because　the　nanoscale　Ta-rich　MX　carbides　that　precipitated　from　the　martensitic　lath　in　the　as-welded　metal　had　an　effect　on　dispersion　strengthening.　This　was　because　the　mass　fraction　of　Ta　corresponded　to　0.26%.　However,　when　the　mass　fraction　of　Ta　increased　from　0.26%　to　0.81%,　the　coarsened　TaC　precipitated　from　the　as-welded　metal　and　was　accompanied　by　the　lath　martensite　and　8-Fe　gradually　disappearing　while　the　content　and　size　of　ferrite　and　pearlite　gradually　increased.　This　resulted　in　a　decline　of　the　impact　toughness.