Metal matrix composites(MMCs)have received much attention due to their promising advanced mechanical properties.The aim of this work is to create a micro-macro model of composite crystallization.The developed model is coupled with the process of heat flow in the macroscopic scale,resulting from the heat emission during the nucleation and the growth of grains.Taking into account both of these phenomena,the proposed model is distinguished by a good reflection of reality.Moreover,the presented model assumes that the function of grain density depends on the maximal supercooling and the mass volume of the reinforcement phase particles.The knowledge of the equations,describing the function of grain density depending on the degree of supercooling,is necessary in the,more and more often used,numerical modelling of the casting structure. Metal matrix composites (MMCs) have received much attention due to their promising advanced mechanical properties. The aim of this work is to create a micro-macro model of composite crystallization. Developed model is coupled with the process of heat flow in the macroscopic scale , resulting from the heat emission during the nucleation and the growth of grains. the proposed model is distinguished by a good reflection of reality. Moreover, the presented model assumes that the function of grain density depends on the maximal supercooling and the mass volume of the reinforcement phase particles. the knowledge of the equations, describing the function of grain density depending on the degree of supercooling, is necessary in the, more and more often used, numerical modeling of the casting structure.