The invention discloses a novel aluminum alloy smokeless two-acid polishing additive and a preparation method thereof. According to the additive, a solution composed of phosphoric acid and pyrophosphoric acid in a certain mass ratio is used as a solvent, sodium molybdate is used as a corrosion inhibitor, copper sulfate and ferric sulfate are used as sensitizers, polyether is used as a dispersing agent, and nicotinic acid is used as a complexing agent. The preparation method comprises the following steps: adding certain amounts of sodium molybdate, copper sulfate, ferric sulfate, nicotinic acid and polyether into the phosphoric acid-pyrophosphoric acid mixture, and dissolving by heating and stirring. The additive does not generate oxynitride yellow smoke or other gaseous pollutants in the traditional three-acid polishing process, thereby preventing the polishing from damaging the human body and environment; and the polishing quality of the additive is comparable with that of the three-acid technique, and thus, the additive is a novel environment-friendly high-efficiency aluminum alloy two-acid polishing additive.