The world-wide increasing demand for the oil and its products and decline in natural production from oilreservoirsand increasing of oil price during recent years have been caused the increasing attention to the production methodsfrom heavy oil reservoirs. As, the main reason of decline in production and exploitation from heavy oil reservoirs isits high viscosity, it can be overcome to this problem by increasing the temperature of reservoir slightly. Meanwhile,the in situ combustion is one of the prevalent thermal methods which have many applications in increasingexploitation from the heavy oil reservoirs. Moreover, as the carbonate stones cannot withstand temperature so muchand may make double problem during in situ combustion, consideration of this process in the carbonate reservoirswhich their number are remarkable in the Middle East countries has been gained significance. During this project, ithas been tried to consider the influence of the effective parameters on this process by modeling. Here, modeling isdone three-dimensionally and considering three phases of oil, water and gas and six components which includedoxygen, water, inert gas, light oil hydrocarbon, heavy oil hydrocarbon and coke. The equations concerning phaseequilibrium and mass equations for each component and energy equation are used as the main equations. Moreoverthese equations, the supporting equations concerning the permeability changes, liquid-vapor equilibrium, calculationof viscosity, porosity of reservoir and qualities of PVT are also used. It has not considered any qualities of stone andconstant fluid to find any slight effect on the recovery of oil. During this modeling, four reactions have been appliedwhich are included coke production of heavy oil hydrocarbon (cracking), oxidation of coke and oxidation of bothcomponents of heavy oil and light hydrocarbon with respect to the thermal limit in the model. The effect ofgeometric qualities of fracture network on the in situ combustion is among the important matters which isremarkable in this modeling. After writing the equations and their discreteness, the finite difference procedure hasbeen used for solving the equation by applying the boundary and initial conditions. By solving these equations themole fraction, oil phase pressure, capillary pressure of water and gas phase can be calculated under varioustemperature and pressure circumstances in different times and finally the rate of recovered oil can be also calculated.After the model made final, the gained results were compared with the experimental results and the results of othermodels; then the effect of different parameters such as density of input oxygen, amount of input oxygen, effect ofpreheating and also the arrangement of fracture and their permeability on the amount of oil recovery wereconsidered after making sure that the model was accurate. During the next phase, the effect of other parameters suchas capillarity pressure, relative permeability and productivity index on the amount of oil recovery were considered.Then, the conditions for the two-dimensional case were developed. Key word: In situ combustion, numerical modeling, simulation, carbonate reservoir.