Abstract: During the welding of AZ31 magnesium alloy plate by GTAW, AC longitudinal and conversion magnetic field were used.The magnetic field current and magnetic field frequency can be adjusted during welding process.Orthogonal experimental design was used to study the effect of parameters on the properties and microstructure of welded joint.The properties of tensile strength and hardness of welded joint were tested.The microstructure of magnesium welded joint was analyzed by metallographic microscope at the same time.The results show that the optimal properties of magnesium alloy welded joint are obtained when welding current is 80 A, magnetic field current is 2 A, and frequency is 20 Hz.