This paper describes design study of the gas turbine engine using PDE as a main combustor of which hydrogen is used as a fuel. In the present analysis, exhaust gas condition of the simple PDE in which no turbine or other obstacles are installed which is estimated by CFD is referred as a turbine inlet condition. About 65 % of enthalpy drop at the exit of the PDE occurs during the exhaust of high temperature combustion gas behind the detonation wave. Furthermore, turbine adiabatic efficiency map of a conventional turbine is taken into account. Approximately, 51-80% of enthalpy drop through the turbine can be extracted as a turbine power. Partial filling of the PDE tube has an effect of smoothing the peak of U/C0.