The invention discloses a real-time tracking control method for a magnetically controlled arc sensing welding seam in gas metal shielded welding, which belongs to a welding control technology. It mainly solves the problems of complex structure, high cost, unstable performance, and poor real-time performance of the existing MIG shielded welding seam tracking system. The key points of its technical scheme are: it includes a magnetically controlled arc sensor, a welding system composed of a welding torch and a welding power supply, a control system, a set of cross carriages and a wheeled robot, and a tracking actuator. The magnetically controlled arc sensor is directly installed on the welding torch of MIGMAW, and collects the lateral and height deviation information of the weld. After signal processing, it is sent to the computer for software processing, and the tracking actuator is controlled in real time to automatically track the weld. This technology realizes the automatic seam tracking of metal gas shielded welding. The magnetron arc sensor is installed on the welding torch of the metal gas shielded welding, without pre- and post-position problems, and has the characteristics of good real-time performance, low cost, high stability and accuracy.