The invention discloses a sewage purification disinfectant and a preparation method thereof. The sewage purification disinfectant is prepared from 30-40 parts of chlorine dioxide aqua, 0.1-0.5 part of bromochlorohydantoin, 0.5-1 part of potassium ferrate, 25-35 parts of aluminum sulfate, 15-25 parts of diatomite, 5-9 parts of tannin, 2-4 parts of lactic acid, 1-2 parts of Lactobacillus acidophilusis, 5-10 parts of brown sugar, 1-2 parts of chitosan, 3-5 parts of acetic acid, 2-4 parts of polyethylenimine, 1-3 parts of dodecyldimethylbenzyl ammonium chloride, 2-4 parts of sodium silicate and 120-160 parts of water. The sewage purification disinfectant has the purifying and bactericidal actions on industrial wastewater, is convenient to use, has favorable scale peeling actions, has the functions of flocculation, deoxidization, corrosion inhibition and sterilization, and has the advantages of less preparation equipment, simple production technique and low investment. The product is harmless to the human body in the production and use process, and can sufficiently satisfy the demands for municipal domestic sewage primary disinfection treatment.