Abstract: Regarding the problem of large cutting loss caused by clustered fine line defects at the edge of dual-phase steel base material for cold rolling, macroscopic and microscopic morphology of defects are analyzed and the hot rolling production process is investigated. The causes of clustered fine line defects at the edges of dual-phase steel base materials for cold rolling have been identified, and targeted improvement measures have been proposed. The results show that the formation of clustered fine line defects at the edge of dual-phase steel base materials for cold rolling is due to the process of roughing rolling. Pit defects are formed when the slab contacts with the vertical roll. Pit defects extend along the rolling direction during the rolling process, forming fine line defects and gradually flip up to the upper surface as the metal flows at the edges and corners of the slab during roughing rolling. After being rolled by a flat roll, edge clustered fine line defects are formed on the surface of dual-phase steel base material for cold rolling. By shortening the vertical roll replacement cycle and adjusting the roughing rolling mode, the clustered fine line defects at the edge of dual-phase steel base material for cold rolling are eliminated, and the quality of the dual-phase steel edge is improved.