The invention discloses a method for preparing phthalic anhydride from 5-hydroxymethylfurfural, and relates to phthalic anhydride. The method comprises the following steps: mixing the biomass platformcompound 5-hydroxymethylfurfural as a reaction substrate with a mixed solvent, an oxidizing agent and a catalyst, performing heating reaction in a sealed manner, and then cooling to room temperatureto obtain reaction liquid of phthalic anhydride, extracting with an extractant immiscible with water, and recovering the extractant to obtain a white needle-like product phthalic anhydride. The methodof synthesizing the important chemical intermediate phthalic anhydride with the renewable biomass platform compound, 5-hydroxymethylfurfural as the reaction substrate, and is a phthalate anhydride synthesis method with high yield, easiness in separation, low cost and low pollution; the catalyst is used in a small amount, a system is simple and efficient, and easy to obtain, reaction conditions are mild, by-products are few, the conversion rate exceeds 99%, and the selectivity is greater than 30%; after purification and recrystallization, the purity of the product is high and exceeds 99.9%.