The paper describes a method to forecast the cohesive zone of blast furnace whose shape is very important for the quality of iron and the efficiency of iron-making industry. This method builds a model that can be observed during the operation of iron making. The model considers that during the chemical reaction the ore, the coke and the gas abide by two equations: the equation of conservation of mass and the equation of heat conservation. Based on this presumption, by dividing the blast furnace into a series of homocentric circles in the height direction and resolving the equations in every homocentric circle with its own parameters, we can get the relationship between temperature and height of the inner blast furnace. And then, according to the fusibility character of the ore, we can forecast the shape and position of the cohesive zone. Finally, the paper visualizes the cohesive zone of blast furnace and discusses some results achieved through the application of such method to a real blast furnace.