Abstract: High speed casting was used to cast the low carbon steel grades used for tinplate due to the narrow width. Sliver defects were frequently detected in tinplate, which caused high downgrade ratio and production cost. The micro analysis revealed that the primary cause of these linear defects was FeO type with small oxide points. Under high casting speeds, the heat flux density of the molten steel exceeded the critical heat flux density, resulting in longitudinal slab cracks, which subsequently evolved into linear defects during rolling. By reducing the Na₂O content to 1.47%, increasing the Li₂O content to 1.7%, and controlling the fluid flow through optimization the current parameters of FC mold, the FeO type sliver defects were sharply decreased.