Abstract: Butt twin-wire submerged arc welding tests under 53-150 kJ/cm welding heat inputs were conducted on Q370qE bridge steel that can resist high welding heat input, and the microstructure characteristics and mechanical properties of the welded joints under various welding heat inputs were also investigated. The experimental results show that the average width of original austenite grains at the center of weld seams grows from 166 μm to 221 μm as the welding heat input increases from 53 kJ/cm to 150 kJ/cm, and the area proportion of proeutectoid ferrite increases from 30.2% to 51.9%, while the area proportion of acicular ferrite decreases from 69.8% to 48.1%. Meanwhile, the average widths of heat affected zone and its coarse-grained zone in welded joints respectively increase by 42.3% and 507.6%, and the contents of acicular ferrite and granular bainite reduce obviously. After increasing the welding heat input to 150 kJ/cm, the welded joint shows obvious softening, while its tensile strength and low-temperature impact toughness fall below the standard values. Meanwhile, the impact fracture surfaces of weld metal and heat affected zone present typical quasi-cleavage fracture characteristics.Furthermore, a full penetration Q370qE bridge steel welded joint of 30 mm thickness can be obtained by respectively welding one pass in the groove of both sides under 100 kJ/cm welding heat input, in which the overall mechanical properties of the welded joint meet the specification requirements. Therefore, the maximum permissible welding heat input of the Q370qE bridge steel can reach nearly 100 kJ/cm in the efficient welding engineering application of future.