The inner structure of the continuously cast semis has a great importance from the point of view of further processing and application. The main reason for this is the very direct effect of the inner structure’s features (ie. porosity, macrosegregations, geometry of primary dendrites) on the technological characteristic features of the semis during further processing (ie. crack sensitivity, formability, etc.). The paper deals with the possible ways of macrostructure determination on the basis of the results of mathematical modeling of continuous casting process. We pay a special attention to the columnar-equiaxed transition as a function of heat parameters of the casting process and to the macrosegregation formation caused by the motion of solute enriched interdendritic liquid in the mushy zone.