In the present work, the calculations of the modified operating line for the COREX process, based on the Rist diagram approach, have been performed. The operating line developed by Rist in 1960's has been modified by various researchers for improvements in the blast furnace. The idea proposed by Rist was further utilized to perform the heat balance along with the net oxygen balance for the other iron making processes. The operating line has been modified thus accounting the generated H2O and CO2 with respect to Fe, in the process of smelting reduction of ore by coal containing volatile and moisture. © 2020 ISIJ.