This welding seam tracker can effectively solve the problems brought about by the welding seam deviation; improve the welding quality and welding efficiency; reduce the welding defects generation; greatly reduce the labor intensity of the welder. It consists of Controller, Sensor, Sensor Cross Regulator, Horizontal Slide, Vertical Slide and Connecting Cables. This system uses high-precision sensor to detect groove shape changes’ signals of the workpiece. Then, send the signals to controller. Controller drives the horizontal slide and vertical slide to control welding torch move quickly and accurately, and thus achieves auto welding tracking. It has been supplied on many kinds of auto welding equipments, for example welding manipulator, gantry welding machine, cantilever welding machine, elbow welding machine, vertical / girth welder, the flange welding machine, submerged arc welding carriage, etc.