The coning phenomenon usually occurs in water and gas cap drive reservoirs. Water coning in Iranian hydrocarbon reservoirs is one of the most important problems that affects the cumulative production, operation costs and causes environmental problems. Before producing from a reservoir, its fluids are in equilibrium and their contact surfaces remain unchanged, but after starting production from the reservoir, when the viscous force overcome gravitational force in vertical direction, contact surfaces will displace and coning will occur. So, the production rates will be controlled in a range that prevents entering water and gas to the production well. For this reason, investigation and modeling of this phenomenon is extremely necessary. In this paper, the coning phenomenon in one of Iranian gas reservoir had simulated using Eclipse 300 software and parameters affecting coning had studied. Results of this work have shown that water production behavior in fractured gas reservoirs is mostly depending on production rate. Also, sensitivity analysis revealed that the sensitivity of coning time to the changes of fracture horizontal permeability is more than changes of matrix horizontal permeability and fracture vertical permeability. In addition, sensitivity of coning time to the fracture porosity changes is more than matrix one.