Abstract: In view of surface longitudinal crack,intermediate crack and center line crack on 360 mm×450 mm continuous casting blooms,the secondary cooling scheme employed in the continuous bloom caster was opti- mized,which included increasing the specific water flow,adjusting the water flow distribution among the sec- ondary cooling zones,so the surface quality and internal quality of bloom improves obviously.The practical op- eration shows that the ratio of longitudinal crack defect due to serious intermediate crack on blooms is decreased from 53.85% to 0.30%,the ratio of center looseness≤1.0 is increased from 74.87% to 99.53%,the free center line crack is increased from 68.83% to 82.77%,the free intermediate crack is increased from 82.95 % to 90.98 %.