Abstract: Gas turbine cycle with high temperature gas-cooled reactor is the main direction of nuclear energy generation, which is with the advantages in terms of the safety and economy. The thermal and physical properties of helium, nitrogen, carbon dioxide and the mixtures were compared and analyzed in this paper. Further more, the heat transfer coefficient, pressure loss and the stage number of turbo-machines have been also compared. Results indicate that taking the mixture of helium and carbon dioxide as the working fluid of gas turbine cycle with high temperature gas-cooled reactor can not only improve the heat transfer coefficient and decrease the stage number of turbo-machinery, but also can limit the pressure loss to a certain level.