The invention provides a finishing agent for disinfecting sewage. The finishing agent comprises the following components in parts by weight: 1 part of chlorine-containing disinfectant and 0.01-0.5 part of bromide-containing compound, wherein the chlorine-containing disinfectant is sodium chlorate, bleaching powder or liquid chlorine; and the bromide-containing compound is one or the mixture of sodium bromide and potassium bromide. According to the finishing agent disclosed by the invention, the chlorine-containing disinfectant and the bromide-containing compound are combined to remarkably reduce the usage amount of the chlorine-containing disinfectant or improve the disinfecting efficiency, reduce the consumption of the disinfectant and reduce the disinfecting and processing cost.