The invention discloses a crab fodder with a water purifying function. The crab fodder with the water purifying function is characterized by comprising the following raw materials in parts by weight: 20-25 parts of wheat embryo, 17-19 parts of water melon seeds, 21-27 parts of tea seed cakes, 18-24 parts of taro, 13-17 parts of whey powder, 5-8 parts of glucose, 4-7 parts of alec, 3-5 parts of a daqu liquor, 6-9 parts of cotton oil, 12-15 parts of grass carp, 19-26 parts of goose liver, 2-5 parts of polyaluminum ferric chloride, 14-18 parts of shii-take, 15-19 parts of carrots, 17-24 parts of cucumbers, 16-19 parts of cherry, 0.2-0.5 part of scutellaria baicalensis, 0.1-0.3 part of rhizoma anemarrhenae, 2-4 parts of endothelium corneum gigeriae galli, 3-6 parts of a phagostimulant and appropriate water. According to the invention, the crab fodder, prepared through the formula disclosed by the invention, is comprehensive in nutrition, the preparation technology is environmentally friendly, the problem that the conventional crab fodder is easy to disperse, resulting in low fodder use ratio and polluted water, is solved, so that the fodder use ratio is improved, and pollution of the cultivation water caused by excessive fodder is reduced; the crab fodder has the functions of insecticide, bacteria resistance and water purification, improves the survival condition of crabs, and increases the yield, quality and the culture benefits.