The utility model relates to a convexity adjustment device for a multi-roll cold-rolling mill, in particular to a convexity adjustment device for a roller used for a sendzimir mill. The convexity adjustment device is characterized in that a driving component is connected to a mounting bracket through a hydraulic cylinder, and the mounting bracket is fixedly arranged on a stander; the piston rod of the hydraulic cylinder is connected with a double-sided rack through a connecting rod, an indicating component is installed on the piston rod of the hydraulic cylinder, and the double-sided rack is meshed with fan-shaped pinion pieces on two groups of supporting roller sets at the upper part in the middle of an execution component. Eccentric rings are installed on the core shafts of the supporting roller sets, the fan-shaped pinion pieces are distributed at the both sides of the eccentric rings and connected with the eccentric rings, the eccentric rings are installed in saddles, and the saddles are arranged at both sides of a back lining bearing. The convexity adjustment device has the advantages that the structure is reasonable, and the use and the adjustment are convenient; the hydraulic operation is complete, the response speed is high, the correction time is short, and the sensitivity is high; the requirement that the roller system of the multi-roll cold-rolling mill has better plate shape adjustment capacity can be met, and the quality of the finished rolling product can be improved.