Thermodynamic properties for an alloy system play an important role in the materials science and engineering.Therefore,theoretical calculations having the flexibility to deal with complexity are very useful and have scientific meaning.The Hoch-Arpshofen model was deduced from physical principles and is applicable to binary,ternary and larger system using its binary interaction parameters only.Calculations of the activities of Fe-based liquid alloys are calculated using Hoch-Arpshofen model from data on the binary subsystems.Results for the activities for Fe-Au-Ni,Fe-Cr-Ni,Fe-Co-Cr and Fe-Co-Ni systems at required temperature are presented by Hoch-Arpshofen model.The average relative errors of prediction are 7.8%,4.5%,4.9% and 2.7%,respectively.It shows that the calculated results are in good agreement with the experimental data except Fe-Au-Ni system,which exhibits strong interaction between unlike atoms.The model provides a simple,reliable and general method for calculating the activities for Fe-based liquid alloys. Thermodynamic properties for an alloy system play an important role in the materials science and engineering.Therefore, theoretical calculations having the flexibility to deal with complexity are very useful and have scientific meaning. The Hoch-Arpshofen model was deduced from physical principles and is applicable to binary, ternary and larger system using its binary interaction parameters only. Calculations of the activities of Fe-based liquid alloys are calculated using Hoch-Arpshofen model from data on the binary subsystem. Results for the activities for Fe-Au-Ni, Fe- Cr-Ni, Fe-Co-Cr and Fe-Co-Ni systems at required temperatures are presented by Hoch-Arpshofen model. Average relative errors of prediction are 7.8%, 4.5%, 4.9% and 2.7%, respectively.It shows that the calculated results are in good agreement with the experimental data except Fe-Au-Ni system, which exhibits strong interaction between ever. the model provides a simple, reliable and general method for calculating the activi ties for Fe-based liquid alloys.