The invention discloses a real-time follow-up technique of a magnetic controlling arc sensing welding line of gas metal arc welding, which belongs to a welding control technique. The invention mainly solves the problems of complex structure, high cost, unstable performance and poor real-time performance, etc, of the prior gas metal arc welding line follow-up system. The invention adopts the technical proposal that the real-time follow-up technique comprises a magnetic controlling voltaic arc sensor, a welding system composed of a welding torch, a welding electric source and so on, a control system, a follow-up actuating mechanism composed of a set of cross sliding guides, a wheel robots and so on; wherein, the magnetic controlling voltaic arc sensor is directly installed on the welding torch, which is used for gas metal-arc welding process, to collect the horizontal and the vertical deviation signals of the welding line; the processed signals are input in a microcomputer for processing by software; the real-time control follow-up actuating mechanism is capable of automatically following up the welding line. The technique achieves automatic following up of the welding line in gas metal arc welding. The magnetic controlling arc sensor is installed on the welding torch used for gas metal-arc welding process, which eliminates the problems of preposing and postposing, and has the characteristics of good real-time performance, low cost, high stable performance and high precision.