It is noted that steam turbine building is evolving toward the creation of powerful steam turbines with high initial steam parameters, and their creation is not possible without the development of highly efficient cooling systems based on three-dimensional thermo-gas-dynamic calculations. Within this study the virtual test stand, based on the ANSYS Fluent 14.0 system, was created to investigate the conjugate heat transfer and thermal state of rotors and discs with forced cooling systems for powerful steam turbines. The module STEAM (as a user-defined function - UDF) is integrated in the virtual test stand, allowing for the properties of steam at high parameters. The calculated results were compared with the experimental data obtained during heat tests of the forced steam cooling system at the existing thermal power plant. The authors give recommendations for the choice of calculation model parameters that provide the balance of accuracy with an error not exceeding 1% of the metal temperature.