At computer modelling of foundry technology it is necessary to consider quantitatively influence of range of composition of casting alloys (within the grade composition of components) on thermophysical and shrinking properties, setting the most probable values of the maintenance of components to raise quality of the computer forecast of thermophysical processes at fixing of casting and formation of shrinkable emptiness. The thermophysical properties of composition have defined on the basis of developed program complexes intended for thermodynamic simulation of an alloy of set structure. As a result of the carried out research a conclusion have drawn on an urgency of the presented analysis.