In the present study, the effects of inlet air cooling on compound cycle performance in a diesel gas turbine engine system where waste heat is used in the composite power system in the sustainable energy system were investigated thermodynamically. The effects of the inlet air cooling the system that enhances power production and the resulting thermal efficiency values were analyzed based on various operational variables gas turbine pressure ratio, diesel engine compression ratio, gas turbine inlet and fresh air inlet temperatures, etc. . The energy losses in each system component were determined and the second law efficiency of the system was determined based on the introduced operational parameters. The gas turbine unit in the model included a gas generator with two compressors and a high-pressure turbine, and a low-pressure power turbine running on a separate shaft. The diesel engine and gas-generator exhaust gases were mixed and expanded in a low-pressure turbine, leading to the production of power with the waste energy. In the cycle, an intake air cooler, an intercooler and a recuperative air pre-heater were used. In the intake air cooling cycle, the power increase was around 15% when the pressure rate of the low-pressure compressor was 3.5. Natural gas was used as fuel in the thermodynamic model. The cycle irreversibilitywas used in the calculations based onthe thermodynamic concepts.