The invention relates to an MC5 steel and a large-sized flattening roll prepared by using the same, and a manufacturing process of the MC5 steel, wherein the MC5 steel comprises the following chemical components in weight percentages: 0.75%-0.90% C, 0.40%-0.80% Si, 0.20%-0.50% Mn, 4.80%-5.20% Cr, 0.30%-0.60% Ni, 0.20%-0.60% Mo, 0.10%-0.20% V, less than or equal to 0.015% P, less than or equal to 0.015% S, less than or equal to 0.20% Cu, less than or equal to 0.01% Al, less than or equal to 0.02% Pb, less than or equal to 0.02% As, less than or equal to 0.02% Sn, less than or equal to 0.02% Sb, less than or equal to 0.02% Bi, less than or equal to 2 ppm of H, less than or equal to 30 ppm of O, less than or equal to 120 ppm of N, and rest being Fe and inevitable impurities; and the MC5 steel is capable of meeting the utilization requirements of high-end metal plate rolling and long service life of the flattening roll.