The invention discloses a gas-shielded welding method for high-strength bridge steel, which comprises the following steps: (1) the high-strength bridge steel with the tensile strength of between 570 and 650MPa and the thickness of 50 millimeters is adopted, a matched welding material is adopted, wherein the tensile strength of a welding wire is 570-660MPa, and the diameter of the welding wire is 1.2 mm; (2) a gas-shielded welding groove adopts a double V-shaped symmetrical groove, the angle of the groove is 60 DEG, and the truncated edge is 2 millimeters; (3) the welding process specification is as follows: the welding current is 23-27 A, the welding voltage is 23-27 V, the welding speed is 30-29 cm/m, the welding heat input is 12-15 kJ/cm, the argon-rich mixed gas metal arc welding with 20 percent of CO2 and 80 percent of Ar is adopted, the flow of gas is 18-20 L/min, no preheating is performed before welding, and no heat treatment is performed after the welding; and (4) the gas-shielded welding adopts multi-layer multi-pass continuous welding, and the interlayer temperature is controlled to between 100 and 150 DEG C. The welding method has the advantages of good welding processing property, simple and convenient operation, applicability, convenience, high efficiency, and energy conservation, and is applicable to the manufacturing, promotion and application of large-span bridge steel of factories.