Abstract: The large plastic distortion occurs in the weld zone for bead-on-plate welding of thin-plate. A non-contact method was proposed to real-time measure the welding distortion in bead-on-plate welding and cooling process based on weak correlation technique of digital image. The study of full-field distortion law and dynamic distortion law of key points were measured in real-time. Bead-on-plate welding of Q235 steel plate by tungsten inert gas (TIG) welding were carried out to explore distortion law. The results show that the distortion in vertical direction is much larger than that in the other two directions. The thin-plate becomes a convex shape in the welding process and then turns to a saddle shape in cooling process. The full-field distortion of thin-plate is larger with welding current being increased. This method can verify the prediction of numerical simulation and reveal the mechanism of welding distortion in thin-plate, and has important guiding significance.