Abstract: The characteristics and reasons of C,Si,Mn,P,S composition segregations in low carbon high sulfur free cutting steel were researched by chemical analysis and hot hydrochloric acid. The results show that the segregation degree of elements (C, Si, Mn, P, S) is between 0.9 and 1.1,S and P elements are negative segregation at the billet center region,and the center area of continuous casting billet is porosity. The analyses show that the center porosity is the main reason of element negative segregations at the center area.