Abstract: The changes of the formation enthalpy of the system were investigated when the properties of any one component of a binary subsystem were affected by the component out of the subsystem. It was found from the simulation of the formation enthalpies of ternary alloys that the changes of the electronegativity and the electron density of one component of the binary subsystem were proportional to the sum of the electronegativity of both in and out of the subsystem. This effect could simply be taken into account in the calculation which was equivalent to the effect on the volume of the component. When more components existed out of the subsystem， the total contribution of their electronegativity could be equivalent to one component. It is shown from the calculation of the formation enthalpy of ternary alloys that the predicting results considering the effects of the three components were better than that using geometrical model and consistent with the experimental results. The method has great significance to the study of the thermodynamic properties of multicomponent system.

Key words: formation enthalpy, model of formation enthalpy, extended Miedema model, binary alloy, multicomponent alloys