In the present paper, a mathematical model has been proposed to describe the behaviour of fluid flow, heat and chemical reactions in an ironmaking blast furnace, in which gas, solid and liquid phases affect each other via interaction forces and their flows are competing for voids. The results show that some critical regions can be predicted, such as the deadman for solid flow and dry zone for liquid flow. Process variables characterizing the internal furnace situation such as reduction degree, reducing gas and burden concentration can be obtained from the model calculation. In particular, the position of impermeable cohesive zone layers, which is of paramount importance to blast furnace operations, can be predicted based on the burden temperature distribution. The model is further applied to understand the effect of operational conditions such as top burden distribution and burden property on fluid flow, heat and chemical reactions in the blast furnace.