Abstarct: During the excavation of tunnels, depending on the type of rock formation which tunnels pass towards them, some gases may release from these formation to tunnel atmosphere which must dilute to allowable limit. One of the gases which its presence has been demonstrated in some Iranian tunnels, is hydrogen sulfide gas. H2S is a very dangerous gas. Allowable level of this gas is 20 ppm. In upper levels, it can causes respiratory paralysis leading to death. Geological formation related to hydrocarbon resources are very important information and reservation of H2S gas. H2S can exist in tunnel in two ways, solved in water and/or as a part of the air environment. Depending on the type of its presence, there are different methods for its dilution or removal with different efficiency. Zagros tunnel, with overall length, 14 km, is a long drilling stage tunnel in Iran. This tunnel is drilling with a TBM machine. during drilling, tunnel mechanical ventilation is done by Longitudinal ventilation. Release of H2S from rock formation of wall tunnel, is a big problem in this tunnel. baxsed on the measurements, amount of solution H2S gas is 11mg/lit in water intake tunnel. Flow of entering water is 170 lit/s. dencity of H2S in tunnel atmosphere is 50-60 ppm. In this study, after the perusing of H2S source in Zagros tunnel, In the firs step, some methods has been given which are requirement to establish better working condition in the TBM and the backup section and can be implemented quickly. Then number of methods has been given either for decrees of water intake tunnel and so reduction of H2S release in tunnel atmosphere, or filtration of entered H2S in tunnel. These measures have major rule to establish better working condition in the TBM and the backup section and also in the access to the TBM from the portal. Logical decision making for selection of one or more method need to Accurate study of them. the AHP method was incorporated to evaluate the optimum option for elimination of H2S emission in tunnel, according to the pre-determined criteria. These criteria are operation time, current and capital cost, efficiency, felexibility, environmental conditions and application of method. Using the AHP method, the grouting method was the most convenient method in Zagros tunnel when the alternatives were evaluated according to the considered criteria. In the last section the technical and economical evaluation of grouting in 7200 Km of Zagros tunnel, with high emission of H2S gas, has been done.