A preparation method of 2,5-diformylfuran, relating to 2,5-diformylfuran, includes: 1) mixing a reaction raw material, a composite catalyst including a main catalyst iron-based compound and a cocatalyst, an oxidant, an oxidization promoter, and a reaction solvent, performing heating reaction in a reactor and cooling the product to room temperature to obtain a 2,5-diformylfuran reaction liquid; 2)cooling the 2,5-diformylfuran reaction liquid to room temperature, filtering the liquid to remove the catalyst, and performing reduced pressure distillation to recover the reaction solvent and preparea slight-yellow powder; 3) dissolving the powder in dichloromethane and washing the dichloromethane solution with a saturated NaCl solution, performing reduced pressure distillation to recover the dichloromethane to obtain a slight-yellow powder, and drying the powder to obtain the 2,5-diformylfuran in a slight yellow color. The preparation method employs easy-to-obtain oxidant and cheap catalystwith low use amount, is high in yield, is gentle in reaction conditions, makes the product easy to separate, is green and economical and has potential industrial value.