In view of the large fluctuation of the gas turbine load in the distributed energy system, the current researches on Organic Rankine Cycle (ORC) pay more attention to the comparison of the thermal performance of the same heat absorption with the initial parameters, but rarely consider the impacts of decrease in both flue gas temperature and mass flow rate on system performance causing by the gas turbine load reduction. Based on the characteristic model constructed by HYSYS platform, optimization scheme of the variable working condition ORC working medium was studied using the narrow⁃point temperature difference in the heat exchanger as the constraint condition. Under the variable load condition of gas⁃fired power plants, the operating parameters of the maximum net output power of the system are optimized. The cycle performances of varies working fluids with different compositions were compared of the characteristics of heat rate, mass flow and AP. The net output of R152a system shows obvious advantages on the heat rate and mass flow rate, compared with that in the mixed working medium in the selected working condition range, while the condenser AP value and the system heat recovery rate exhibit opposite performance. This work provides a reference database for the studying of the binary non⁃azeotropic mixture of ORC system.