Automatic or semi-automatic welding methods are required for improving efficiency and safety, then various seam tracking technologies have been developed as an important part of them. For laser welding, although industrial application is magnifying widely, traditional seam-tracking technologies are difficult to apply. We have developed new monitoring system of weld zone and its around at the same time under high luminosity of laser welding, using the 2nd harmonics generator of pulsed YAG laser for illuminating the situation of weld. Using this system, we can observe the welding situations clearly in monitors, even for especially high luminous welding phenomenon, such a laser welding. Using this system, we have developed the seam tracking control system of laser welding by analyzing the images in computer in order to decide the position of the weld line and beam point and conducting tbe feedback coontrol of laser torch position. For examining this system, we conducted the I-bat welding on stainless steel plate changing welding track and welding speed. Through the experiment, followings were understood. This system can use high speed welding and works sufficiently in laser welding.