Due to the technological requirements and layout characteristics of thermal power plants, the tail water of once-through cooling water system usually has the characteristics of large flow and rich residual energy. Engineering practice has shown that the recovery of residual energy can be effectively carried out with the help of small hydro turbines. Combined with a coastal power plant as an example, based on the study of the drainage characteristics and the tail water residual energy of the cooling system in the thermal power plant, the scheme design and economic analysis of the tail water residual energy power generation in a typical thermal power plant are carried out. The results show that it is feasible and reasonable to use the residual energy of the tail water in the power plant, which provides an alternative solution for the utilization of the residual energy of the tail water in the thermal power plant.