The well-known continuous casting method, the roll casting process, has been widely used to produce slabs, billets and blooms. But it suffers from low productivity to casting unsoundness due to three major limiting factors centerline segregation, sticking and heat line formation. In this paper, a numerical study for the roll casting process has been performed on the basis of enthalpy method to understand the phenomenon of defects formations as well as to predict the interface locations, the temperature fields of the solid, liquid and mushy regions with different feed speeds. Several different cases are examined. Numerical studies exhibit that the exit slab temperatures are functions of the casting speeds and the aspect ratios. If the casting speed exceeds a certain critical casting speed, the centerline slab temperature can be catastropically increased, then the defects might be formed.