The invention discloses a method for preparing 1-oxo-1,3-dihydro-3-hydroxybenzofuran-5-formic acid. The method disclosed by the invention comprises the following steps: dissolving 2,5-toluene dihalideinto a tetrahydrofuran solution, carrying out a reaction with magnesium metal under iodine catalysis so as to obtain a corresponding Grignard reagent, and introducing carbon dioxide so as to obtain 2-methylterephthalic acid; performing chromium trioxide oxidation and diluted hydrochloric acid hydrolysis on the 2-methylterephthalic acid in the presence of glacial acetic acid, acetic anhydride andconcentrated sulfuric acid so as to prepare the 1-oxo-1,3-dihydro-3-hydroxybenzofuran-5-formic acid. The preparation method disclosed by the invention is simple in synthesis, cheap and readily available in raw material and convenient for large-scale preparation, reaction treatment in the invention is simple, and a pure target product can be obtained by virtue of washing, extracting and filtering only. Moreover, requirements on reaction instruments and equipment are simple, and since the raw materials are cheap and readily available, the method has great advantages on reaction cost, improves economic benefits and has excellent industrial prospects.