The crack healing process during hot rolling has been investigated. According to the experimental results, the crack healing process goes through four stages: crack surface contact, locally healing discontinuously, healing zone expanding, and global healing. On the basis of above results, the mechanism of crack healing is established. A new concept of crack contact depth is proposed. When the crack contact depth is less than a critical value, the continuity of crack is broken by the action of atoms near crack surfaces which might be caused by the movement of dislocation during deformation, and a local zone heals, then the healing zone expands.