In this paper by using numerical evaluation the effect of balancing drupes of water hammer on tunnels lining is considered. In case of not arrangment of these reservoirs, the tunnel lining will be damaged of cyclic powers of water hammer. In this research, function of balancing reservoir of water hammer on cover of tunnels to the barriers’ turbine is simulated by numerical methods and Plaxis 3D Tunnel, the RocSupport and the Roclab software. In numerical investigation, input spectrum of quasi-sine of water hammer is used. The results of this research show if there isn't use of balancing reservoir of water hammer, plastic radius of the tunnel sides is increased by 105%; and in case of usage of balancing reservoir of water hummer, the plastic radius is decreased only by 5%. Therefore, in water transmission tunnels under pressure for turbines, usage of balancing reservoir of water hammer are strongly recommended.