Abstract: The effect of solidification structure on the centerline segregation and flow of molten steel has been studied based on the steel production and the solidification structure.The interface of solidification goes ahead regularly and the solutes concentrate on the center of slabs,which cause the segregation.But if the columnar crystals are developed and the solutes rest on the interspace of columnar crystals,the centerline segregation can be improved.The solidification interface of equiaxed grains can spread the solutes around it,which can improve the centerline segregation,but when the phenomena of molten steel complementing the solidification shrinkage happens in the region of equiaxed grains,it will worsen the centerline segregation.