Abstract: How the inversed surface segregation of P forms in strip casting was discussed by structure observing and analyzing, and its effects on the mechanical properties of twin roll cast strips were investigated through tests. The results showed that a homogeneous P-rich surface layer forms on the strip after cold rolling and annealing. The percentage elongation of conventional strips will drastically decrease if P content is over 0.15%, but it will be kept to about 30% if P content is 0.26%. It means that the twin roll strip casting process can raise the P tolerance in strip by about 0.1%. In addition, the ductile-brittle transition temperature (DBTT) of the cast strips is lower than that of conventional strips though the P content is the same.