The invention discloses a compound medicament for separating crude proteins from monosodium glutamate-fermented waste liquor and a preparation method thereof. The preparation method comprises the following steps of: adding 42.63 g/kg of sodium metasilicate nonahydrate solids and 858.6 g/kg of water to a reactor at room temperature, rapidly stirring for uniformly mixing, and diluting to a solutionwith the silicon dioxide concentration of 1%; then adding sulfuric acid to the reactor to acidize the solution to the pH value of 1-1.5, and standing for 2 min; stabilizing the molar ratio (Al<3+>+Fe<3+>)/SiO2 of 1.5, then adding 18.1 g/kg-40.74 g/kg of aluminum chloride hexahydrate and 15.2 g/kg-40.54 g/kg of ferric trichloride hexahydrate according to different Al3/Fe<3+> molar ratio of 0.5-2; stirring for 5 min in the high rotation speed of 850r/min for uniformly mixing to produce polysilicate aluminum ferrite chloride with different proportions; and finally adding 20 g/kg -30 g/kg of chitosan and 12.83 g/kg-20.13 g/kg of starch, stirring for 5 min in the high rotation speed of 850 r/min and curing for 1 hour to produce the compound medicament with different proportions. The compound medicament has the advantages of wide source of raw materials, less consumption, safety, no toxicity and simple process and reduces the concentrations of organic pollutants in the waste liquor when recovering the crude proteins from monosodium glutamate-fermented waste liquor.