The invention discloses a welding seam tracking system and a welding seam tracking method. The welding seam tracking system comprises a vision sensing device, a bracket, a welding gun, a movement mechanism, a computer and a baffle, wherein the vision sensing device comprises a spot laser, a line laser and an area-array camera; the area-array camera collects images and transmits the collected images to the computer; the computer gives a command to control the movement mechanism to move in three-dimensional directions, so that during the welding process, the height of the welding gun can be automatically adjusted by monitoring the altitude changes of the workpiece surface. According to the welding seam tracking system and the welding seam tracking method, the welding seam height recognition tracking method and the welding gun adjusting method which are integrated based on the dot and line lasers is firstly adopted, the tracking method has a better adaptability to various working conditions, the limitation of the tracking method in the prior art is overcome, the response speed of the method is high, the altitude changes of the workpiece surface can be accurately identified, the accuracy is high, and the welding seam tracking can be completed high efficiently.