The invention discloses a method for synthesis of a 4H-pyrrolo[3,2-c]pyridin-4-one compound. The method comprises that 2-arylamino-N-arylpyrrole compound and an aldehyde compound as raw materials and PEG-400 as a solvent undergo a reaction in the presence of ammonium acetate as a catalyst under the condition of heating to produce the 4H-pyrrolo[3,2-c]pyridin-4-one compound, and the product is cooled and is subjected to pumping filtration separation so that a 4H-pyrrolo[3,2-c]pyridin-4-one compound finished product is obtained. The method has one reaction step, has a simple process, utilizes cheap and easily available raw materials, catalyst and solvent, has the advantages of high reaction efficiency, simple operation, good function group compatibility, good area selectivity and high product yield and has a wide application prospect.