In this paper, the calculation of a combined cycle including a gas and steam circuits with two nuclear reactors is done. The first circuit of the thermal scheme is the gas cycle with a very high temperature reactor (VHTR) and the second circuit of the combined scheme is the steam cycle with the pressurized water reactor (VVER). VHTR which is one circuit reactor and uses Helium as a coolant and working fluid and VVER is a two circuit reactor which uses water as a coolant and steam as working fluid. The scheme was limited by the parameters of the two reactors and aimed at reaching the highest thermal efficiency of the power of the two reactors. The calculations showed the effect of changing the parameters of one reactor side to the other reactor side, on the total efficiency and power output. These parameters are the thermal power of VHTR core and the compression ratio of the gas turbine and their effect on the steam turbine power output, the steam cycle efficiency, the gas turbine power output and the gas cycle efficiency. Finally, the results showed high thermal efficiency of the scheme comparing to the two the thermal efficiencies of each single cycle.