Abstract: In this research, considering the experiments of tunnel inflow due to 10 different tunnels in Iran and adopting idea from site geomechanics rating like RMR, a new method has been developed for rating the tunnel site to evaluate the potential of tunnel inflow according to the preliminary investigation data. This method is called Site Groundwater Rating (SGR). Considered parameters in this method are: joint frequency, joint aperture, karstification, crashed zone, schistosity, head of water above tunnel, soil permeability and annual raining. Using these parameters and following SGR method, tunnel site can be categorized into six rates as follow: no risk, low risk, moderate risk, risky, high risk and critical. The method has been checked out with the observed groundwater inflow of Ghomroud tunnel and also, implied to rate the Amirkabir tunnel site in Iran.