The invention relates to a method for preparing tetrahydro-2-ethyl anthraquinone from a working solution for the production of hydrogen peroxide by anthraquinone process, comprising the following steps: taking a certain amount of the working solution for the production of hydrogen peroxide by anthraquinone process to conduct vacuum distillation, removing heavy aromatics and other substances of low boiling point to obtain a dried substances; carrying out oversaturated dissolving on the obtained dried substances with organic solvents, stirring, oscillating, conducting suction filtration, letting trioctyl phosphate and 2-ethyl anthraquinone, etc. in the solvent, drying insoluble substances to obtain dried substances; dissolving the dried substances with organic solvents, and conducting recrystallization to obtain high-purity tetrahydro-2-ethyl anthraquinone. The method of the invention not only solves the problems of time consuming and labor consuming property and low conversion rate when synthesizing tetrahydro-2-ethyl anthraquinone by autoclave reaction, but also reduces the cost, shortens the operation time. Tetrahydro-2-ethyl anthraquinone prepared by the method of the invention has a purity of more than 99.5%, and can be used as a tetrahydro-2-ethyl anthraquinone standard sample for analyzing the working solution for hydrogen peroxide.