Abstract: Significant differences in thermal crown of work rolls occur in a 20-high mill of a steel plant due to different configurations of the cooling system for upper and lower roll assemblies, resulting in poor flatness of the rolled strip. To solve this problem, this paper first establishes a flatness prediction model considering the asymmetric thermal roll profile of the upper and lower roll systems of the 20-high mill, and systematically analyzes the influence of the original roll profiles of the work rolls and first intermediate rolls on the strip flatness. On this basis, a multi-objective control function is constructed, which takes the coincidence degree between the actual strip flatness and the target flatness as the core objective, and simultaneously considers the stress concentration of inter-roll pressure and the suppression of edge thinning. An optimization design method for the original crown of the work rolls and the end taper of the first intermediate rolls of the 20-high mill is formed. After applying this method to on-site production practice, the flatness control ability of the rolling mill is improved, and the flatness problem caused by the asymmetry of the thermal roll profiles of the upper and lower roll systems is solved. The on-site application shows that the average flatness of the finished strip is reduced from 15.3 IU to 8.5 IU, and the flatness improvement effect is significant.