This paper describes the design of a 300MW HTGR-GT power plant which was completed in the framework of the HTGR-GT feasibility study project. The project is assigned to JAERI by the Science and Technology Agency of Japan. The inlet and outlet gas temperatures in the reactor are 550°C and 900°C, respectively. Helium gas pressure is 6MPa. The turbine system is a recuperative intercooled direct cycle one. Designs of helium turbine, LP and HP compressors and generator are presented, whose adiabatic efficiencies are 93.09, 89.92 and 90.25%, respectively. A horizontal single-shaft configuration was adopted whose rotor dynamics is given.Copyright © 2000 by ASME