Abstarct: Pump-storage power plant is located in Lorestan province and adjacent Roudbar reservoir located in 92 kilometers south of the city Aligoodarz. To evaluate the potential of hydroelectric energy generation capacity of 1500 MW electricity to the national grid, electricity consumption during peak hours (early hours of the night) is designing and running. Plant will be inside the mountain. For this purpose, the structure as the main cavern will be built underground. Height, width and length of the powerhouse cavern are respectively, 50, 24.5 and 120 m. Powerhouse cavern will be in the rocks of the Dalan Formation that is a sequence of limestone and dolomite limestone . In this thesis, the stability of structure have been studied baxsed on drilling process using experimental,structural and numerical methods. The powerhouse cavern drilling operations has been done in the nine-step numerical analysis. FLAC 3D software is used for numerical analysis that is baxsed on the FDM method. To stability analysis of powerhouse cavern in without support condition is used Sakurai critical strain method. Stability analysis of powerhouse cavern using the above methods are obtained the following results. The software outputs are included the amount of horizontal, vertical deformations and safety factor values for surrounding structure and analysis of support system that used in power plant cavern. To increase the stability of power plant cavern, The installation of shotcrete reinforced with steel mesh, two laxyers of springs 10*10 cm and a thickness of 20 cm has been suggested.