Abstract: The pulsed MIG welding was used to weld AZ31B Mg alloy, and the weldability of the alloy was studied.The microstructure, mechanical property and hardness of the welded joint were investigated via the metal phase microscopy, scanning electron microscope, tensile testing machine and hardness instrument.The results show that one-side welding with back can be obtained through this technique at optimized parameters when there was no groove and no shaped ban, which continuous butt joints have no surface defects.The heat-affected zone of the joints is narrow, and the grains of the zone are slightly larger than that of the base metal.The grains of fusion zone are tiny, the microstructure is homogeneous and the hardness of welded joint is higher than that of the base metal.The tensile strength is up to 95% of the base metal.