Organic Rankine Cycle is one of the most promising technologies for low-temperature energy conversion. In recent years, it has gotten more attention due to the energy crisis and environmental problems caused by the combustion of fossil fuels. A lot of research has been done on low-grade energy conversion systems based on Organic Rankine Cycles, and several optimization methods have been proposed. In this study, correlative literatures are reviewed and the efficiency improving strategies are elucidated. Guidelines for the promotion of this low-temperature heat conversion system are also presented.