<p>Tungsten inert gas (TIG) arc employed direct current electrode negative, and metal inert gas (MIG) arc employed direct current electrode positive. By arranging the two arcs at an appropriate spacing along the welding direction, a hybrid TIG-MIG (HTM) arc was formed, which was an effective technique to solve the welding problem by combining the merits of TIG and MIG arcs. However, the interaction of arcs complicated the HTM process, making it challenging to select appropriate welding parameters. A multi-physics coupled numerical model for the HTM arc was established to investigate its behaviors, disregarding the droplet and molten pool. The distribution of current density, temperature, electromagnetic force, velocity, and pressure was analyzed in detail. The results indicated that a direct current path was established between the welding wire and the tungsten electrode, resulting in the merging of the original MIG and TIG arcs, which coupled to form the hybrid HTM arc. The electromagnetic repulsion force generated by the reverse current caused the original arcs to deflect along the welding direction, and the shape of the HTM arc was a bimodal distribution. Compared with the traditional single arc, the thermal influence range of the HTM arc on the workpiece surface expanded both along and perpendicular to the welding direction, reducing the temperature gradient and the cooling rate of molten metal behind the arc, which was beneficial to filling the weld toe. As the TIG current increased, the potential difference between the welding wire and the tungsten electrode increased, which led to an augmentation in the current flux between them. This, in turn, diminished the electromagnetic force, thereby reducing the plasma velocity and weakening the arc pressure acting on the molten pool. The above thermal-pressure characteristics of the HTM arc were beneficial to suppressing the occurrence of undercut and humping defects in high-speed welding, achieving high-quality and high-efficiency welding.</p>