According to the mechanism of the crack produced by the joint action of the three elements of the cold crack in the welding of high strength steel,the technical connotation of the crack is analyzed in detail,and the mechanism of the delayed crack is mainly analyzed. The application project is illustrated. The special type of "transverse crack" in the cold crack is also described in detail. At the same time,the treatment scheme of welding cold crack in a project of high strength steel is put forward. On the basis of successful treatment,the method to prevent welding cold cracks is proposed;and the viewpoints that are easily misunderstood are demonstrated;therefore,it is valuable to prevent cold crack in high strength steel.