The invention relates to an automatic tracking control and online correction system with a welding gun and a control method thereof and belongs to the technical field of robotic arc welding. The automatic tracking and control and online correction system comprises a vision sensing system, an image processing system, a tracking control system and an online correction system, wherein the vision sensing system comprises a CCD (Charge Coupled Device) vision sensor; the image processing system comprises an image preprocessing module and an image processing module; the tracking control system comprises the welding gun, a control system, a driving system, a signal processing module and an arc sensor; the online correction system comprises a laser two-dimensional outline scanning sensor and an error analysis module. According to the automatic tracking control and online correction system, butt-welded seams are predicated, tracked and corrected respectively a prewelding stage, a welding stage and a post-welding stage by virtue of error online fusion of three sensors, namely the CCD vision sensor, the arc sensor and the laser two-dimensional outline scanning sensor, so that the welded seam tracking precision and the fault tolerance of the system are improved, the welding production efficiency and the welding quality are improved, and the automatic tracking control and online correction system has generality.