Abstarct: Pressure tunnels with high internal pressures are constructed in hydropower projects. This pressure sometimes increases and passes allowable value. In this condition, the rock mass can not suffer this pressure, so it is essential to be used a lining for transporting a fraction of this pressure to rock mass and resisting against rest pressure. In more details, the aim of this thesis is to design a steel lining reinforcement for the pressure tunnel nearby of the penstank well. In the first stage, designing process has been done baxsed on the Schliess equations. After that, ignoring some aspects governing the problem, ABAQUS software has been used for the numerical modeling of the problem. Finally, considering the instabilities, proper reinforcement is determined for the cement covering the steel lining using by PCACOL software. It can also be mentioned that in this research work, thickness of the pipes in the pressure tunnel and distance of pads has been designed baxsed on the transported water. Steel lining design has also done with relying on the buckling theory.