A mathematical model coupling the momentum, energy and species conservation equa-tions was proposed to calculate the macro--segregation of Fe--C alloy ingot during solid-ification. The corresponding simulation software which concurrently solves the macro-scopic mass, momentum, energy and species conservation equations has been developedby applying the SIMPLE algorithm.The thermo--solutal convection in a NH_4 Cl--H_2O ingot is verified and the result showsgood agreement with that reported. Then macro--segregation in a steel ingot is simu-lated by using the developed program. The steel ingot is in a rectangular mold with ariser. The fluid flow is mainly induced by the temperature field and the solid fraction.The macro--segregation pattern is mainly affected by the thermo--induced convectionin the mushy zone. The negative segregation forms along the walls of the casting.The positive segregation forms at the top center of the casting into the riser. Thespecies concentration reaches the peak in the center of A mathematical model coupling the momentum, energy and species conservation equa-tions was proposed to calculate the macro - segregation of Fe - C alloy ingot during solid -ification. The corresponding simulation software which concurrently solves the macro-scopic mass, momentum, energy and species conservation equations has been developed by applying the SIMPLE algorithm. The thermo - solutal convection in a NH_4 Cl - H_2O ingot is verified and the result showsgood agreement with that reported. Then macro - segregation in a steel ingot is simu- lated by using the developed program. The steel ingot is in a rectangular mold with ariser. The fluid flow is mainly induced by the temperature field and the solid fraction. The macro - segregation pattern is primarily affected by the thermo - induced convectionin the The negative segregation forms along the walls of the casting. The positive segregation forms at the top center of the casting into the riser. Thespecies concentration reaches the pea k in the center of