The invention discloses a treating agent for efficiently treating domestic sewage and a preparation method thereof, and the treating agent comprises the following raw materials by weight: 10-45 parts of polyacrylamide, 10-50 parts of diatomite, 1-20 parts of activated carbon, 10-60 parts of sodium aluminate, 10-50 parts of lignin, 1-15 parts of ferrous sulfate, 5-30 parts of aluminum sulfate, 5-30 parts of bentonite, 5-35 parts of ferric trichloride, 5-35 parts of ethylenediamine tetraacetic acid disodium salt, 3-30 parts of hide glue butyl acrylate, 5-35 parts of rectorite, 1-12 parts of sorbitol fatty acid ester, 0.5-10 parts of sulfosuccinic acid and 0.05-4 parts of ferric chloride. The method is as follows: adding water into the diatomite and the bentonite to obtain mixed slurry, adding the activated carbon, the lignin, the aluminum sulfate, the ferric trichloride, the hide glue butyl acrylate and the rectorite for mixing evenly, stacking, performing ultrasound treatment, evenly mixing with remaining raw materials, stirring to obtain pulp, and drying to obtain the treating agent. The physical and chemical indexes of the domestic sewage can reach the GB18918 2002 standard, the treatment process is simple, the dosage is low, the treatment effect is good, the performance is stable, and the effluent quality is good.