Abstract: The inverse problem and its solving method of organic Rankine cycle（ORC） system provide a efficiency and simply way for analyzing performance of ORC system. In this paper, toluene, MDM, benzene, cyclohexane, heptane, MM,hexane, isohexane were selected as working fluids based on the inverse problem of ORC system driven by two different heat sources, 573.15 K and 523.15 K. With the pinch temperature difference as constraints, the optimum operating conditions and properties of working fluids were obtained through calculating thermal efficiency and exergy efficiency, and the variation of net work output, mass flow and operating pressure was compared. The results show that Toluene, Benzene and Cyclohexane are suit for both of two heat sources. Hexane only suit for ORC system driven by lower heat source, 523.15 K.