Welding wire for gas protective welding of reduced activation ferritic/martensitic steel and the manufacturing method, chemical components (weight percentage, wt %): C: 0.10.15, Cr: 8.09.0, W: 1.01.6, V: 0.150.25, Ta: 0.100.17, Mn: 0.500.70, Si: 00.05, N: 00.02, O, Ni, Cu, Al, and Co: 00.01 respectively, P, S, Ag, Mo, and Nb: 00.005 respectively, and balance of Fe. The welding wire has Cr equivalent weight of less than 11, Ni equivalent weight of greater than 3.5. It is manufactured with a wire rod through multi-pass drawing. The rod is subject to annealing heat treatment, tempering treatment performed between the passes of drawing. The annealing process is: the rod is at 9401020 for 2060 minutes, and the n cooled to below 650 C. at rate of less than 45 C./hour, air-cooled to room temperature. The tempering process is: the rod is at 760820 for 0.52 hours. It reduces forming of ferrites in welded joints.