The invention provides a sewage disinfector, and a preparation method and application method thereof. The sewage disinfector comprises, by mass, 40 to 60% of potassium monopersulfate, 0 to 5% of calcium peroxide, 4 to 15% of magnesium sulfate, 6 to 12% of iron chloride, 5 to 15% of sodium bicarbonate, 0 to 7% of nanometer titanium dioxide, 0 to 10% of chitosan, 0 to 12% of starch xanthate, 3 to 8% of fatty acid monoglyceride, 4 to 20% of a weak acid component and 1 to 15% of a stabilizing agent. After dissolving of the sewage disinfector provided by the invention, a plurality of high-activity free radicals are continuously produced and exert combined disinfection effect, so the sewage disinfector has the advantages of a wide disinfection spectrum, good disinfection effect, high efficiency and safety; through combined usage of three flocculating agents consisting of iron chloride, chitosan and starch xanthate, the sewage disinfector can remove metal ions, radioactive substances and organic matters in water and effectively decrease CODs and BODs in a water body; and nanometer titanium dioxide can kill a plurality of bacteria and fungi in water in long duration and is free of toxicity and harm. When the sewage disinfector is applied to treatment of sewage, procedures like grating filtering, fermentation, precipitation and flotation are not necessarily needed, so the sewage disinfector is convenient to use.