Through the analysis of the magnetic field around the arc, the feasibility of controlling the arc shape and performance by the external axial magnetic field is clarified. Combined with the derived mathematical expression of the alternating axial magnetic field generated by the energized solenoid, the magnetic field and its distribution were simulated with COMSOL Multiphysics and MATLAB software, and the effects of the magnetic head structure and parameters on the magnetic field and its distribution were determined. A magnetic head was designed and manufactured according to the simulation results, and the welding process experiments were carried out. The experimental results show that the high-frequency axial magnetic field can significantly compress the arc and improve the welding penetration.