The tendency of welding cracks of X80 steel involved in the slit type cracking test was discussed. The results show that the section crack rate of X80 pipeline steel decreases with the increase of the preheating temperature of the workpiece,the shape and nature of cracks that are cracked at the root stress concentration and distributed along the fusion zone are hydrogen-induced cold cracks. The area has become the weak link of the joint when the cold crack three factors are focused on the coarse-grained zone of the fusion zone of X80 pipeline steel,so it is easy to form cracks on the area. The microstructure characteristics of fusion zone are the necessary condition of the cracks to form in the influencing factors,the stress level and distribution characteristics of hydrogen are sufficient conditions. The relationship between the welding process and cracking essentially reflects the relationship between hydrogen,stress and crack in weld metal. The comprehensive processes of low hydrogenation with minimizing residual diffusion hydrogen in the weld metal and insufficient to cause hydrogen-induced cold cracks are often used in engineering,and have achieved satisfactory results.