The invention discloses a method for synthesizing acetic acid. The method comprises the following steps: putting ethanol, carbon dioxide and hydrogen gas into a reaction kettle and reacting in the presence of ruthenium complex and rhodium complex catalysts, an organic ligand, an iodide cocatalyst and a solvent, so as to obtain the acetic acid. The invention reports a reaction route for the first time and a homogeneous phase catalysis system is innovatively utilized to realize the reaction in a high-activity and high-selectivity manner under a relatively mild condition. The catalysts are easy to circularly utilize and have extremely great industrialization development value. The method disclosed by the invention has important significance on recycling of the carbon dioxide and alleviation of environment problems caused by the carbon dioxide.