Abstract: The exergy losses and thermodynamic efficiency of MSF plant with brine recirculation are discussed by means of temperature difference functions proposed by the author. In a MSF plant, the irreversible losses are found mainly in irreversible heat-transfer and flash evaporation processes. However, the basic variables are the temperature drop from stage to stage, and the temperature differences between flashed vapor and cooling water. In this paper, the flash temperature difference function, the heat transfer TD function, and the total TD function are suggested. The proposed TD functions of MSF plant provide a convenient tool toanalyse the irreversible behavior and evaluate the thermodynamic efficiency of this system, because without such improvement the calculation of the thermodynamic efficiency of a MSF plant according to the classical formula will be not only inconvenient but also insignificant. As a result of present analysis, the reasonable parameters based on the energy consumption are easily chosen. The above-mentioned principles are confirmed by typical commercial plants and a pilot plant in Tianjin.