Nowadays graphene is a famous material that most researchers are working on its quality and domain size. One of the common methods that we can synthesize graphene with high quality and larger size is Chemical Vapor Deposition (CVD) method. In CVD process for graphene formation, reaction and process conditions affect the production rate of graphene. Pressure, temperature, substrate and partial pressure of reactant are these conditions that can vary along the CVD reactor. Simulation of this process can help scientists, researchers and engineers in understanding, developing and scale upping of these systems. In this investigation several factors that can affect the synthesis of graphene by using CVD has been studied. For illustration these factors, the process simulated by using Computational Fluid Dynamic (CFD) method and the commercial software, ANSYS Fluent 13. The methane was used as hydrocarbon precursor in presence of hydrogen, and argon as carrier gas with the flow rate of 0.5, 5 and 100 sccm, . The simulation was performed in various pressures and the temperature was varied from 700 to 1000 °C. 21 gas phase reactions and 8 surface reactions were considered. Among the various factors that have effects on the graphene growth, the gas phase component, the growth temperature, the operating pressure, the inlet concentration of hydrocarbon precursor gas and substrate site that are more important, was studied. First the temperature and velocity profiles in the reactor were illustrated, and then the gas species were analyzed. The result showed that at the beginning of the reactor, reactions did not perform duo to the low temperature but with increasing temperature, methane start to pyrolyze and produce several species. Among these species CH 3 and H were studied because of their importance. The graphene area coverage was considered as output parameter for studying how the temperature, the operating pressure, the inlet concentration of hydrocarbon precursor and the substrate site affect graphene growth. The result showed that increasing the temperature from 993 to 1273 °K, increase the graphene area coverage up to 77 percent. Also with moving toward the end of the reactor, the graphene area coverage increase. Also increasing the pressure first decreases the coverage then increases it. In the case of the inlet methane concentration, results showed that increasing the concentration, increases the surface coverage. Finally, by using the Surface Response Methodology and Box-Behnken Design, optimum condition for 100 percent coverage of graphene predicted for CVD proce 1185 °K, 413 Pa and the inlet molar fraction of 0.009 for methane. Keywords CVD, Graphene growth, Area coverage, CFD, Methane pyrolysis.