Abstract: In plasma-pulse metal inert gas welding (Plasma-PMIG), the strong electromagnetic repulsive force between arcs of opposite polarities severely diminishes the stiffness and deep penetration characteristics of the plasma arc. Given that traditional constant magnetic fields struggle to adapt to the dynamic changes in repulsive force caused by the drastic fluctuations of the PMIG pulse current, a regulation and control method of synchronous magnetic field was proposed to achieve flexible coupling between the dual arcs. A synchronous magnetic field control device was developed to output magnetic field voltages matched with the pulse peak and base values by monitoring the edges of the PMIG current waveform in real time. By combining XIRIS high-speed imaging with FLUENT numerical simulation, a three-dimensional magnetohydrodynamic model was established to investigate the dynamic effects of synchronous magnetic field voltage on the arc morphology and temperature field during the welding of 304 stainless steel. The results indicate that the Lorentz force generated by the synchronous magnetic field can dynamically counteract the electromagnetic repulsive force. When the magnetic field voltage is 36 V, the Lorentz force and the repulsive force reach an optimal balance during the peak phase, allowing the plasma arc to remain perpendicular and enhancing its stiffness. This technology realizes dynamic flexible coupling of the dual arcs, eliminating serpentine weld seams and spattering. Under optimal parameters, the weld penetration increases by 22.1%, significantly improving the stability of mass and heat transfer processes and substantially enhancing the formation quality.