The invention provides a preparation method of 2,5-furandicarboxylic acid. The preparation method comprises the following steps: A), with non-grain biomass as a raw material, preparing furfural; B), oxidizing the furfural to obtain furoic acid; C), performing an addition reaction on the furoic acid and carbon dioxide under the action of a catalyst to obtain the 2,5-furandicarboxylic acid, whereinthe catalyst is one or more of potassium carbonate, sodium oxalate, sodium nitrate, potassium nitrate, sodium nitrite, potassium nitrite, potassium acetate, sodium acetate, potassium formate, sodium formate, sodium hydrogen carbonate, potassium hydrogen carbonate, sodium hydroxide and potassium hydroxide. The furfural is prepared from the non-grain biomass as the raw material, so that the raw material cost is low; the furoic acid reacts with the carbon dioxide under the action of the specific catalyst to obtain the 2,5-furandicarboxylic acid; the catalyst is low in price; the used carbon dioxide is environment-friendly; by the preparation method, the yield is high.