The invention provides an environment-friendly recovered grease decolorizing agent and a preparation method thereof. The environment-friendly recovered grease decolorizing agent is prepared from the following ingredients: water washing acidification rice hull ash, non-water washing-acidification rice hull ash, carbonized soybean hull ash, chitosan, dodecyl dimethyl benzyl ammonium chloride, epigallocatechin gallate, dilauryl thiodipropionate, sorbic acid, butyl p-hydroxybenzoate, ethyl alcohol, hydrochloric acid and water. The preparation method is characterized in that firstly, the chitosan, the hydrochloric acid and the water are mixed, and the mixture is stirred by a magnetic stirrer to obtain a solution A; the sorbic acid, the butyl p-hydroxybenzoate and the ethyl alcohol are mixed and stirred to obtain a solution B; then, the rest ingredients, the solution A and the solution B are mixed, and are then stirred by the magnetic stirrer to be put into a drying box to be dried. The environment-friendly recovered grease decolorizing agent has the advantages that the decolorizing can be fast and effectively performed; meanwhile, partial metal ions are removed; the peroxide value is reduced; the recovered grease quality is improved; in addition, the preparation method is simple and is suitable for industrial production.