The invention discloses a hand-held roller surface slag clearing device. The hand-held roller surface slag clearing device comprises a polishing table board, a polishing mechanism and a foreign matteradsorption channel, the polishing table board is arranged on the outer peripheral surface of a roller, the polishing mechanism is arranged on the polishing table board, the working surface of the polishing mechanism can make contact with the roller surface of the roller, the foreign matter adsorption channel is vertically arranged, one side of an upper opening of the foreign matter adsorption channel is connected to the lower side edge of the polishing table board, and the other side of the upper opening of the foreign matter adsorption channel extends to the roller surface of the roller. Theinvention further provides an on-line roller surface foreign matter clearing method. Compared with the prior art, the slag clearing device and method have the beneficial effects that foreign matter on the roller surface of the roller can be polished and cleared by utilizing a gap of a charging and discharging sleeve without shutdown, shutdown for roller replacement is not needed, the surface quality of a steel strip is guaranteed, and meanwhile, the production efficiency of a unit is improved; and the clearing device is simple in structure, relatively small in volume, high in slag removal efficiency and applicable to any cold rolling production line.