Abstract: In order to ensure the water production capacity of the seawater desalination system under the low load condition of the generator units, and improve the economy of the whole plant, four dual-purpose power and water plant units were taken as examples. The thermodynamic modeling of the four units was carried out by EBSILON software, and the accuracy of the model was verified. The steam sources meeting the conditions of sea fresh water production were analyzed, and three steam extraction schemes meeting the conditions of low load were put forward. Based on the classical theory of thermodynamics, the thermodynamic model was used to demonstrate and analyze the three steam extraction schemes. Moreover, through the comparative analysis of the coal consumption and transformation cost of the three steam extraction schemes, the optimal low load steam supply scheme was obtained. This study has a certain guiding significance for the power plant energy saving and emission reduction and improvement of the economic efficiency of power plant operation.