The invention belongs to the field of ultra-supercritical power station welding materials and particularly relates to a solution strengthening type nickel base alloy welding wire high in plasticity. The solution strengthening type nickel base alloy welding wire is suitable for welding of ultra-supercritical boiler superheaters/reheater pipes, welding between the superheaters and boiler gas collection headers (including connecting pipe seats) and welding between the reheater pipes and the boiler gas collection headers (including the connecting pipe seats). The solution strengthening type nickel base alloy welding wire is mainly characterized in that after the welding wire is used in welding conducted through TIG welding (argon tungsten-arc welding), weld deposit metal can be recrystallized after being subjected to postweld heat treatment at the temperature of 1000 DEG C or higher, and dendrite and columnar crystal tissue in an original weld is removed; the hardness of a weld area after welding is 300 HV, and the hardness is reduced to 210 HV after recrystallization; and weld residual stress and component segregation are eliminated, and the welding wire is basically consistent with base metal in appearance. The chemical components of the nickel base alloy welding wire include, by weight percent, smaller than 3% of Fe, 14%-18% of Cr, smaller than or equal to 0.45% of Al and Ti, smaller than 0.9% of Ti/Al, 1.0%-1.5% of Nb, 7.0%-9.8% of Mo, smaller than 0.4% of W, smaller than or equal to 1.0% of Si, 0.5%-1.0% of Mn, smaller than or equal to 0.1% of C, 0.003%-0.005% of B, smaller than or equal to 0.03% of Zr, the balance Ni and smaller than 0.1% of the sum of other impurity elements.