The invention discloses flux cores for high heat-input electro-gas welding gas protection welding wires. The flux cores are prepared, by mass percent, by the chemical constituents of 1-3% of at least one of titanium dioxide and rutile, 3-7% of at least one of quartz sand, feldspar and zircon sand, 1-4% of at least one of marble, dolomite and magnesite, 1-3% of at least one of lithium carbonate, sodium carbonate and potassium carbonate, 14-20% of low-carbon ferromanganese, 1-4% of ferromolybdenum, 4-8% of nickel powder, 2-5% of ferrotitanium, 1-5% of rare-earth silicon, 0.01-0.05% of boron powder and the balance iron powder. The invention further discloses the gas protection welding wires for high heat-input electro-gas welding, each gas protection welding wire comprises a steel jacket and the corresponding flux core which is coated with the steel jacket, and the flux core is any one of the flux cores for the high heat-input electro-gas welding gas protection welding wires. The invention further discloses weld deposited metal which is obtained by adopting any one of the gas protection welding wires to conduct welding.