The campaign life of an iron blast furnace depends on hearth wear. Distributions of liquid iron flow and refractory temperatures have a significant influence on hearth wear. A 3D comprehensive computational fluid dynamics model has been developed specifically for simulating the blast furnace hearth. It includes both the hot metal flow and the conjugate heat transfer through the refractories. The model has been extensively validated using measurement data from Mittal Steel old, new IH7 blast furnace and U.S. Steel 13 blast furnace. Good agreements between measured and calculated refractory temperature profiles have been achieved. It has been used to analyze the velocity and temperature distributions and wear patterns of different furnaces and operating conditions. The results can be used to predict the inner profile of hearth and to provide guidance for protecting the hearth.