Centerline segregation is of practical significance since it affects the material properties. Center- line segregation in continuous casting billets was studied by solving the fluid flow, solidification, and solute transport equations from the initially liquid steel to the completely solid state using the finite difference method with the SIMPLER algorithm. The results show that the centerline segregation is induced by both the fluid flow in the mushy zone and the accumulation of solute-rich liquid near the solidification front. The species concentration in the center of the strand rises quickly in the mushy region to a maximum at the end of solidification. The most serious segregation occurs along the billet centerline. Centerline segregation is of practical significance since it affects the material properties. Center-line segregation in continuous casting billets was studied by solving the fluid flow, solidification, and solute transport equations from the initially liquid steel to the completely solid state using the finite difference method with the SIMPLER algorithm. The results show that the centerline segregation is induced by both the fluid flow in the mushy zone and the accumulation of solute-rich liquid near the solidification front. The species concentration in the center of the strand rises quickly in the mushy region to a maximum at the end of solidification. The most serious segregation occurs along the billet centerline.