Many national energy projects have been pursued in Japan. Some of them are very important to control the emission Of CO2 from fossil fuel. The world energy network (WE-NET) project based on a hydrogen combustion gas turbine is one of the national projects and has a high target of thermal efficiency up to 60% or more (HHV) [Proc. IJPGC, Vol. 2, Baltimore, 1998, p. 293; Proc. IJPGC, Vol. 2, Baltimore, 1998, p. 433; Annual Summary Report on WE-NET, 1997; J. JSME, 100 (947) (1997) 1034; J. GTSJ, 27 (4) (1999) 217]. However, this new technology has to be developed by an application of a combined cycle for gas and steam turbines and special auxiliary equipment such as an oxygen supply plant and heat exchangers. The hydrogen combustion gas turbine will be operated by pure hydrogen and oxygen supplied and kept to produce a pure water vapor only. If other gaseous components are included in the combustion gas, the thermal efficiency of the combined cycle is decreased by the breakdown effect of a condenser vacuum. In this project, hydrogen may be imported from some foreign countries where it has to be produced by using clean and renewable energies, for example, hydropower or solar energy. On the other hand, the oxygen to be distilled from the air has to be supplied by auxiliary equipment of a liquid oxygen plant. This auxiliary equipment, however, will consume much power. In an existing type of the liquid oxygen plant, about 10% of the total power plant output has been consumed for the additional power of oxygen supply. In addition, the WE-NET combined cycle of the hydrogen combustion gas turbine will be supported by many heat exchangers that have to be checked for their technical problems. This paper has been highlighted at high performance design and setup of the major auxiliary equipment of the oxygen supply plant and the heat exchangers. The R&D prospect of their auxiliary equipment to attain a high thermal efficiency of the combined cycle in the WE-NET project will be discussed.