Abstract: Thermodynamic analysis on power cycle parameters is generally the basis of parameter configuration, system design and off-design performance. Based on the design parameters of the practical distributed energy supply systems with gas-steam combined cycle, consisting of typical industrial type, aeroengine modified-type and heavy-duty gas turbines below 114 MW capacity, the empirical coupling relation between the power efficiency of bottom cycle and the exhaust temperature of turbine was summarized. The thermo-economic analysis parameters and model were proposed suitably for the energy supply system. Using the proposed method, the influence of design parameters on the design performance of the energy supply system was obtained. It concludes that, the concept of unit power deficiency coefficient by extraction steam obtains a concise and meaningful expression of comprehensive thermal efficiency. At a given designed heat/power ratio and heating parameters, compressor optimal pressure ratio at the maximum comprehensive thermal efficiency is considered equal to that at the maximum power efficiency of combined cycle. The system has a higher comprehensive thermal efficiency in the case of a lower grade of steam for heating/cooling. The expectation value of electrical power price of the distributed energy supply system is relatively higher. Improving turbine inlet gas temperature is an important direction for enhancing the thermal economy of the system. This research presents a basis for the off-design performance analysis and the price linkage mechanism between power/heating/cooling and natural gas.