Abstract: Based on the "three rolls with different diameters" design,modification was conducted to the hot-rolling strip mill.A driven minor working roll was placed between the original two rolls,allowing the work-piece to go along the pass formed by the original lower working roll and the said minor roll,thus reducing the rolling pressure by 49%~62%. With the modified mill,thinner strip with better eveness,straightness and finish are available. Also briefed here are the process features,operation and economic profitibility of the modified mill.