The present work shows the possibility of using Thermo-Calc software for computer modeling with the aim to predict the phase transformation processes in cast aluminum-silicon alloys with small alloying of iron up to 0.5% by weight. These alloys are widely used in many industries, such as engineering, aircraft, chemical technology, construction and others. The paper describes the relationship between the experimental results of analysis of structural state of alloys obtained by melting in the laboratory and the modeled data in Thermo-Calc software. Modeling of the phase composition of alloys does not allow obtaining information about the real components of the structure, but allows predicting the temperature intervals in which the phase transformations occur during the formation of the structure under cooling. The obtained temperature limits of the existence of each phase show how the concentration of silicon in the alloys changes: it decreases in all phases when the alloy is cooled. All alloys are characterized by a narrow interval of crystallization. Computer modeling allows to make a choice of new compositions of alloys and technologies for their experimental production on the basis of simulated diagrams.