NOVELTY - The system comprises a domestic sewage pipeline, an urban regenerated water outlet pipeline and a biochemical treatment device. An end of the biochemical treatment device is formed with an opening of the domestic sewage pipe. Another end of the domestic sewage system is connected with an outlet and an inlet of the urban regenerated water outlet pipeline, which is connected with an outlet of a circulation cooling device of an engine of the biochemical treatment device. An inlet of the buffer water tank is connected with the urban regenerated water outlet pipeline.    USE - The system is useful for supplementing water to the circulation cooling device of a thermal power plant (claimed).    ADVANTAGE - The system improves the biodegradability of the urban regenerated water by performing biochemical treatment on the domestic sewage and the urban regenerated water.    DETAILED DESCRIPTION - The system comprises a domestic sewage pipeline, an urban regenerated water outlet pipeline and a biochemical treatment device. An end of the biochemical treatment device is formed with an opening of the domestic sewage pipe. Another end of the domestic sewage system is connected with an outlet and an inlet of the urban regenerated water outlet pipeline, which is connected with an outlet of a circulation cooling device of an engine of the biochemical treatment device. The biochemical treatment device comprises a circulation cooling water tank. The domestic sewage pipeline is connected with the biochemical treatment device. The urban regenerated water outlet pipeline regenerates water into the biochemical treatment device, which comprises a biological aerated filter tank, a buffer water tank and a lifting pump. Ends of the biological aerated filter tank are provided with openings of domestic sewage pipeline, respectively. An inlet of the buffer water tank is connected with the urban regenerated water outlet pipeline. An opening is formed with the outlet of the biological aerated filter tank is connected with the water tank, the circulation cooling device and heat air outlet of the biological aerated filter tank. The lifting pump is provided between the biological aerated filter tank and the buffer water tank. An INDEPENDENT CLAIM is included for a method of supplementing water to the circulation cooling device of a thermal power plant.