Abstract: In the process of gas shielded arc welding (GMAW), it is a direct way to increase the welding deposit rate by adopting high wire feeding speed, increasing welding current and dry elongation. However, when the droplet transfer is changed into rotating jet transfer, the arc is unstable, the spatter increases and the weld formation becomes worse. A longitudinal alternating magnetic field with different frequencies is applied to control the weld formation. The arc shape and droplet transfer during welding were photographed by high-speed video camera. The effects of magnetic field with different frequencies on droplet transfer and welding spatter rate were studied. The results show that the mechanism of spatter is different with different droplet transfer modes; when the applied frequency is 1 000 Hz longitudinal alternating magnetic field, the rotating radius of arc decreases, the stiffness of arc increases, the arc is more stable, the welding spatter rate decreases, and the weld shape is improved.