Abstract: An agglomerated flux with high-basicity, low-activity and ultra-low diffused hydrogen was prepared, and the tensile test, V-Charpy test and drop-weight test were practiced for the welding metal deposited by low alloyed wire with the flux. By analyzing microstructure of welding metal, the mechanism that the deposited welding metal reaches high toughness was elucidated. By the measurement of diffused hydrogen content of welding metal and the property of anti-cold crack in Barton crack test, the flux was evaluated.