Abstarct: Water inflow is one of the main problems in constructing of underground space during constructing and utilizing steps. This problem decreases the ability of the operative group and consequently increasing the costs and decreasing the advance rate. Accurate predicting the value of the inflow in different steps of construction will increase the ability of the operative group to control the inflow. Zagros long tunnel is one of the projects that is so hard to excavate because of water inflow. This tunnel with 26km lengh passed the hydrocarbon formations and jointed rock mass, and is a part of water conveyance project in the west tropical plains of Iran. The estimation of inflow jointed rock mass is convoluted because of jointed properties such as orientation and spacing. In this study the behavior of underground water in fractured rock and then analytic and empirical methods in tunnel inflow will discussed. In this methods pendency of permeability that estimated in field testing and assumption such as continuous rock mass will make error in result. For better estimation of inflow in this tunnel, estimation will solve by distinct element method numerically by UDEC software. The results of numerical estimation have a better corrolation with real data from tunnel inflow. Inflow was predicted by use of calibrated model in the areas that is not excavated now. By use of parametric analysis, the aperture, spacing, orientation of the joint and underground water level analysed. In the end of this study control systems of inflow will discuss and offer a method for control of water in this project.