Abstract: The gas shielded arc welding process and weld joint impact toughness of an ultrafine grained steel plate with 380MPa yield strength and 520MPa tensile strength were studied.The welding by both sides could be carried out at 200~300A weld current,24~33V weld voltage and 16.3cm/min weld velocity with almost no weld cracks.The effect of electric current on the impact toughness of weld was much more remarkable than on that of other parts in weld joint when operated at above 250A,the weld toughness increased obviously,and weld width also increased with almost no influence on the width of HAZ.