The invention provides a magnetism-control rotary electric arc sensor with an effect of converging an electric arc through a magnetic field. The magnetism-control rotary electric arc sensor can be used for surface repairing of a complex curved surface, seam tracking of automatic welding and solving problems that electric arc divergence is unstable, an electric arc transition angle is large, electric arc heat is not concentrated and the like in the current magnetic-control rotary electric arc sensor. The sensor comprises a seal-capping body, an inverted conical lower shell body which is used for replacing an air cover and fixing a magnetic pole, an oil conveying pipe for conveying cooling oil, a magnetic pole group for generating a transverse magnetic field on the horizontal plane and the vertical plane, a soft iron sleeve sleeving on the magnetic pole and a bakelite plug for fixing the magnetic pole. The sensor is in the inverted conical shape, so that the structure is simple and compact, and the accessibility is good; and the electric arc can be subjected to magnetic convergence, mechanical compression and thermal compression, and therefore the electric arc can be stably deflected during welding, the electric arc can be converged at the same time, the electric arc stiffness can be improved, the stability of the sensor signals is improved, the heat efficiency of the welding of the electric arc is improved, and the productivity is improved.