Abstarct: In this study, selection of optimum primary support system was investigated for Beheshtabad water transporting tunnel. Beheshtabad water transporting tunnel approximately with 65 kilometers length and 6 meters width is one of the biggest water supplying project for transporting water to central plateau of Iran. The most important properties that effect on the tunneling operation are the weak constructions of tunnel and issues under the water table. Selection a suitable support system in order to stability of rock mass and reduction of plasticity zone around the tunnel area is the most important issue of this project designing. In this study 6 types of support system has been considered as a possibility option for this tunnel and by using FLAC2D software amount of displacement and safety factor for each of the option is calculated. Then by using fuzzy Analytical Hierarchy Process (FAHP) and by considering sex creation include cost, safety factor, time, applicability factor, displacement and mechanization, the optimum support system has been selected. In this study we showed that injection rock bolt with 3 meter in length and 1/5*1/5 spacing with 10 centimeter shotcrete is the best support system for this tunnel. Then the statistical distribution curve of ground profile is drowned by using Crystal Ball software also by using Rocsupport software probability of failure and reliability of system has been calculated. They were 25.12 and 74.8 percent respectively.