A shaft structure of a rotor tail end (10) of a gas turbine in which a steam passage (20) for supplying and recovering a steam for cooling rotor blades of the gas turbine extends along a center axis of the rotor assembly of the gas turbine, wherein a center hole of the rotor tail end (10) coaxial to the center axis of the steam passage is formed in the rotor tail end (10). Provision is also made of a thermal sleeve (16) between the steam passage (20) and the inner surface of the center hole (15) of the rotor tail end (10), so that a thermal insulation gas layer (18) is formed between the inner surface of the center hole of the rotor tail end (10) and the thermal sleeve (16). The thermal insulation gas layer (18) is isolated gas-tightly and liquid-tightly from the outside. <IMAGE>
