Abstract: Studied are the microstructure and impact resistance of the low carbon bainite steel welded joint presenting under the conditions of different heat inputs.Relevant testing results show that after being butt seam welded, the weld microstructure of the said steel is of both acicular ferrite and granular bainite, while the HAZ microstructure is of bainite-ferrite and granular bainite, and the grains of both the weld zone and the HAZ are reduced along with decrease of the heat input.The weld fracture type is in most cases a ductile one, and the weld impact resistance is rather good in any case.When the welding heat input is being increased from 24.8 kJ/cm to 28.2 kJ/cm, the impact energy of the weld zone and the HAZ present a trend of first decreasing, and then increasing.