In order to resolve the problems existing in the application of the water networks integration optimization method in the thermal power plant, the transfer process of mass impurities from water regeneration units was expanded in this study. The complete mass transfer process was used to describe the process of water utilization of impurity load units, and the maximum mass transfer capacity and rate of regeneration are used to describe the processes of regeneration. In addition, a directed graph was used to describe the connections between units of water networks. Through analyzing the relationship between the maximum concentration, impurity load, and water supply process of water units, the mathematical mechanism of the optimization process was obtained so as to build a regeneration recycling water networks optimization model. A 3300 MW thermal power plant was chosen to conduct model application research. The water networks of the case power plant was divided into 9 water subsystems, and equivalently divided into 11 water units, then a concentration correction model had been constructed for the regeneration unit to achieve the maximum mass removal process. The chloride ion, entire solids of suspended matter, and sulfate ion were picked to perform a water-saving optimization design, and the model was simplified by solving the KKT conditions of the optimization problem. After optimization, the use of fresh water of the water networks was reduced by 6.7%, total emissions of sewage were reduced by 62.9%. The case study showed that the constructed regeneration recycling water networks model based on the "supply-utilization-consumption-discharge" process of water networks was successful, and it could realize the water-saving optimization design of the water networks in thermal power plants considering multiple impurities. Furthermore, it resolved the issues of inaccuracy in the description of the regeneration process in the use of the integrated optimization method of water networks in thermal power plants, as well as the inappropriate description of the water regeneration unit for water-saving reconstruction of water networks.