The invention discloses a welding wire for alternating-current submerged-arc welding of 2.25Cr-1Mo-0.25V steel. The welding wire is characterized by comprising, by mass, 0.07-0.20% of C, 0-0.3% of Si,0.5-1.6% of Mn, 0-0.010% of P, 0-0.010% of S, 2.00-2.60% of Cr, 0.90-1.15% of Mo, 0.30-0.41% of V, 0.01-0.04% of Nb, 0-0.15% of Cu, 0-0.10% of Ni, 0-0.005% of Sb, 0-0.006% of Sn, 0-0.008% of As, 0-0.02% of Ti, 0-0.01% of B, 0-0.007% of O, 0-0.010% of N and the balance Fe. A welding flux comprises, by mass, 21-37% of magnesium oxide, 3-10% of silicon dioxide, 7-21% of calcium oxide, 10-21% of aluminum oxide, 5.7-22.7% of carbonate, 6.5-21% of fluorite, 0-3% of potassium feldspar, 0-2% of electrolytic manganese, 0-1% of ferrosilicon and 0-2.5% of aluminum powder. The welding wire and the welding flux have the advantages that the welding wire is used with the welding flux, and accordingly larger weld width can be obtained in a welding process under an alternating-current submerged-arc welding process; when thick walls are welded, effective sidewall bonding is facilitated, weld metal after welding is high in low-temperature impact toughness and highly resistant to cracks.