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 it is the very direct effect of the inner structure's features (i.e. porosity, macrosegregations, geometry of primary dendrites) on the technological characteristics features of the semis during further processing (i.e. 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 paid special attention to the geometry of primary dendrites and to the columnar-equiaxed transition as a function of heat parameters of the casting process.