A method for synthesizing molybdenum-vanadium-tellurium-niobium oxide by sequential microwave irradiation, comprising the steps of irradiating a polar solvent in microwave; adding precursors of molybdenum, vanadium, tellurium and niobium successively into the polar solvent to obtain a mixed solution; re-irradiating the mixture solution after each addition of the precursors to obtain a slurry; adjusting the pH of the slurry; drying the slurry to form a solid; and calcining the solid to obtain the molybdenum-vanadium-tellurium-niobium oxide.