Abstract: The analysis of the mass and enthalpy balances is made for the smelting reduction process in the two-stage of shaft furnace-iron bath. Because of the relevance to carbonaceous as well as hydrogenaceous gases in the process, the Fe-C-O-H₂ system is employed. The two combining equations of the oxygen balance and the enthalpy balance for prereduction and smelting reduction reactors are formulated respectively- Two equations can be related reasonably by means of calculating thermodynamic results and the Rist diagram of the process is figured out. The mathematical model is developed for calculating the fuel rate, oxygen consumed and other control parameters for the process.