Abstract: Longitudinal direct-current magnetic field is used in TIG (tungsten inert-gas)welding of AZ31 magnesium alloy to improve the welding property of magnesium alloy, the influence of different magnetic current on welded joint is analyzed.It is found that the joint is texture varied apparently after magnetic field is added. The microstructure in weld is refined.Lots of sphere-like second phase particles appear on the grain boundary and the quantity increases apparently, the microstructure in HAZ (heat-affected zone) is also refined.The quantity of second-phase is decreased from weld to HAZ.It is revealed that weld consists of α-Mg and β-Al₁₂Mg₁₇ by X-ray diffraction.With proper processing parameter, when the magnetic current is 4 A, the tensile strength and hardness of welded joint are increased apparently, thus the mechanical properties of welded joint of AZ31 magnesium alloy are increased.