Abstarct: Chamshir Dam and power plant has been designed to control Floodwater, agricultural activities, hydroelectric power generation. This Dam is under construction on Zohre River and located in Kohgiluyeh and Boyer Ahmad. According to the position of the cavern and discontinuities, the instability in this huge space would disrupt the performance of the structure during the operation, the stability analysis and design of support system for gate chamber is necessary. Firstly, using experimental methods RMR and Q, were classified rock mass of gate chamber and temporary support were estimated. In addition these approaches, using numerical methods, discrete element method and software 3DEC, modeling and stability analysis of gate chamber was conducted considering different discontinuities.To investigate the priority of these strength properties of rock and joint in the stability of gate chamber, a sensitivity analysis has been performed. Finally, proper support system of sprayed concrete and rock bolt was verified for gate chamber. Support system includes sprayed concrete thickness of 15 cm and rock bolt diameter of 32 mm with a length of 8 meters spacing 2×2 in walls and 1.5×2 on the roof. Most displacement occurred in the left side wall. The results of modelling include the trend of displacement according to the results of field instrumentation. After support system installation decreases displacements about 41 percent.