This research article reports simulations and prediction based calculation for Co-Fe system under the application of Calphad method and thermo-calc package. At different elevated temperature of 1200k, 1225k 1nd 1250k the said system is modeled and corresponding behavior of Gibbs free energy, phase diagram and activity curve is monitored. As per calculation the Gibbs energy curve is correspond to its negative era which shows the actual stability application of the said alloy system. The alloying element shows strong interaction amongst which results negative deviation from Roults law in activity era. At 1250k the activity value becomes maximum with same negative deviation. This shows the applicability and reliability of the said alloy system.