System simulation for COREX process not only gives guidance for its development, but also produces a theoretical basis for the design of its computer control system. A composite model for computational analysis on COREX process of ironmaking has been developed. The model combines a set of common material and heat balance equations, chemical equilibrium equations, and other considered correlations.These equations or correlations are coupled together through the material flows and energy flows between each two of all reactors in COREX process. All parameters are calculated based on one ton hot metal. The consumptions of ore and flux, the quantity of slag, and the composition of slag are calculated using the mass conservation for the element of Fe and the oxides such as CaO、MgO、SiO2、Al2O3、MnO and P2O5, etc. The gas volume and composition are calculated using the mass conservation for the elements of C and H and the chemical equilibrium of watergas reaction, etc. The O2 consumption is calculated using the conservation of the element O. The coal consumption is calculated by using of heat balance for the meltergasifier.