The invention relates to the technical field of steel strip processing, in particular to a protective paper attaching device capable of automatically adapting the width of the steel strip, including a base and an unwinding mechanism, the unwinding mechanism including a turntable, a support column and a drive assembly, and a controller , an attachment mechanism and a cutting mechanism, the attachment mechanism is arranged on the top of the base to attach the protective paper to the surface of the steel strip, the attachment mechanism includes a set of rollers, a slide plate, a pressing assembly, a flattening assembly and a traction assembly, the said The cutting mechanism is set on the side of the attaching mechanism to cut the leftover material on the surface of the steel strip. The cutting mechanism includes a support frame, a pushing component and two cutters, a pressing component, a flattening component, a traction component, a pushing component and a controller They are all electrically connected. The protective paper attaching device and working method that can automatically adapt to the width of the steel strip of the present invention can cut the leftovers of the protective paper for steel strips of different widths, and at the same time has its own pressing function to ensure The protective paper adheres effectively and avoids creasing.