Abstarct: Pollution caused by increasing population and urban traffics in metropolises has become to a national dilemma. Researches show that rail way transport system is the best solution in order to decrease the air pollution in Iran. Hence, constructing urban tunnels is the only way to develop railway system. Considering the costs of tunnel constructing, identifying the risks ahead of tunneling and evaluating the stability and safety related issues are essential in all three steps of design, implementation and operation. As a result, reaching the continuous development in transportation infrastructures could be achieved. Consequently, recognizing, evaluating, managing and controlling the uncertain hazards should be assessed. In this thesis, information of Line No.7 subway tunnel of Tehran has been used for stability analysis of subway tunnels in operational step. To this purpose, firstly, 22 parameters affecting on tunnel stability have been identified. Secondly, Utilizing experts judgment method, Stability index has been introduced. First, the importance of each of the parameters affecting the tunnel stability at the time of operation for the Tehran Metro line 7 tunnel has been identified. The parameters of inflation and ponding, groundwater level and earthquake are the most important parameters, and the parameters of the river, the quality of the materials used And contiguous bridges are the least important parameters in the sustainability of Tehran Metro Line 7 tunnel during operation. The results show that, zone No.16 (km 16+900 to 17+500) and zone No.20 (km 21+130 to 22+000) include higher stability index and could be used as passive defense constructions. On the other hand, zone No. 1 (km 7+500 to 7+860), zone No. 5 (km 8+800 to 9+160) and zone No. 17 (km 17+500 to 19+170) have had low stability index. Also, the ratio of the reduction in useful life of the tunnel compared to the baxse tunnel (tunnel with all the parameters affecting the stability of the tunnel at the time of operation with a maximum score) is on average 19.62%.