viscosity Reduction furnace which aims to reduce the viscosity of the core materials, vacuum and atmospheric residue from the tower to blend with fuel oil produced at some refineries in Iran such as Tehran, Arak and Abadan is installed and working. In the furnace, the heat of the combustion gases from the burner to heat the feed displacement and the reaction temperature leads to thermal decomposition reaction of pure radiation with high viscosity paraffinic chains are long, and it makes the product lighter. In this unit, the severity of cracking is not high, because the high intensity can cause unstable ingredients in the products. The purpose of this operation is to reduce viscosity the fuel, without significant change in the stability of the fuel. This resulted in the most severe thermal cracking to lower feeds resulting in the production of gasoline and lighter materials are reduced to less than 10%. Due to the growing interest in simulating chemical processes, chemical engineers, and construction of the project feed the furnaces and furnace simulation is examined. In these simulation profiles of temperature, pressure, products, raw material and other operating parameters of the pipeline are obtained. The results with the selection of an optimal kinetic models by Castellanos et al, based on a set of sub-components of feed divided by the number of carbon atoms modal and the numerical solution of the mass balance and energy than conventional numerical methods (RK) on the elements of a given length in a tube furnace of the displacement of the beam as an ideal reactor, respectively. The simulated data were compared with experimental data for the refinery furnaces decrease viscosity and consistency of results is acceptable.