Abstract: 20 mm thick Q345qENH rare earth high performance bridge steel plate was welded by CO₂ gas-shield welding and submerged arc welding, respectively. The microstructure and mechanical properties of the welded joints were studied. The results show that the microstructure of weld zone of the two welded joints are proeutectoid ferrite, acicular ferrite and granular bainite, the microstructure of fine grain HAZ are ferrite and granular bainite, the microstructure of coarse grain HAZ welded by CO₂ gas shielded welding are bainite and a small amount of granular bainite, the microstructure of coarse grain HAZ welded by submerged arc welding is bainite. The two joints have good tensile properties, impact properties and cold bending properties, the hardness of HAZ is the highest, which can meet the technical standard of bridge steel, the cold crack tendency of joint is small, and the weldability is good.