Abstract: Taking the welding arc of 6061 aluminum alloy magnetically controlled gas tungsten arc welding (GTAW) as the research object, the three-dimensional model of GTAW welding was established. The changes of welding arc current density, Lorentz force and temperature field without external magnetic field and with external transverse magnetic field were compared and analyzed. The results show that when the magnetic field is not applied, the arc has high symmetry. The maximum value of internal current density reaches 2.66×10⁷ A/m², the Lorentz force reaches 1.21×10⁵ N, and the maximum arc temperature reaches 14 862.4 K. The current density in radial direction is unimodal distributed, and the Lorentz force is bimodal distributed.With the application of transverse magnetic field, the arc deflects, and the Lorentz force increases rapidly.When the magnetic field intensity is 0.2 mT, the maximum value of Lorentz force increases to 1.51×10⁵ N. After deflection, the arc length increases, the potential increases.