Abstarct: Groundwater leakage is one of major factors that may cause negative impacts on tunnel excavation process as well as utilization. Then, issue subject always should be carefully investigated. Grouting is an economical and effective process in order to improve rock mass characterization, such as permeability and thereby a reduction of water flows. The purpose of this type of grouting is to achieve a competent zone, wide enough around the tunnel periphery to prevent water leakage. This thesis is intending to provide an efficient water-tightening grouting process for Karaj water conveyance tunnel (lot I). Meanwhile, this thesis offers grouting pattern, in order to achieve to this target effectively. In the first step, permeability of tunnel in critical areas has been estimated by analytical methods. Obtained results have been shown a good accordance with numerical and empirical models. Then design parameters of water-tightening grouting system have been set up baxsed on the overall outcomes. Considering practical limitations and available technologies using cement-baxsed grouting, the analysis results have been clearly shown that water leakage can effectively reduced, which is good enough at this stage.