Abstarct: The growing trend for using underground space in recent years is due to increasing urban population and the lack of surface areas for development of transportation systems. Most of the great cities are settled on grounds that are not geologically desirable thus some difficulties are inherited in tunneling in urban areas. Tunnel face stability is of great importance in both conventional and mechanized (TBM) methods of construction. Insufficient face support pressure will result in face collapse and surface subsidence while excessive amounts of support pressure may cause surface upheaval which the latter only occurs in case of pressurized shield implementation. In the present research face stability condition of tunnel in Line 3 of Tehran subway is investigated by means of simulation process and numerical method. In the simulation process a probability distribution function is fitted to the values of each important soil parameter then random numbers are assigned to the inverse form of the functions in order to produce random data (Monte Carlo technique). Thus the random data are put into the equations of analytical and experimental methods to give values of support pressure and the factor of safety. In the end the probability of factor of safety being less than a predetermined value is calculated for every amount of applied support pressure. For the numerical method finite element PLAXIS3D Tunnel software is used for tunnel face stability evaluation. The resulted values of face support pressure against collapse are compared to the real values leads to the superiority of results from the method of Broere to the other solution. In the absence of actual values the results of face support pressure against blow-out from simulation process are compared to the numerical results. The results of numerical and Balthaus method are in good agreement.