Abstract: A novel all-fiber optic integration type of weld seam image sensing system with line-structure light projection is put forward,which the optical projection field of line-structure light is produced by integration of an optic transmission fiber and a minitype cylinder lens,and the laser image of weld seam is received with an image transmission fiber bundle.The near-field intensity distribution of the large core quartz fiber-optic transmission surface and the characteristic of the fiber bundle transmitting the laser image of welding seam are analyzed with the ray theory.The theory analysis indicates that the laser transmitted through the large core fiber optic helps to improve the quality of the projection stripe;the great mass of image noise can be filtered after the laser image of weld seam is transmitted by the image transmission fiber optic due to the spatial filtering effect.The experiment results are accordance with the theory analysis in the main.