Abstract: D physicochemical stratiform cloud model was modified and developed to couple with gaseous and aqueous chemical mechanisms as well as with radiation transfer. Precipitation acidification is simulated under the condition of average polluted atmosphere in Eastern China by using this model. The results show that the photolysis coefficient has a factor of 2-3 at cloud top and only 0.2 in cloud base, compared with that in cloudless condition. The role of radical to oxidize S(Ⅳ) in precipitation is exceed H₂O₂, which results in sulfate and nitrate concentration increasing gradually in later term of precipitation. Thus ground rainwater is getting more and more acidic due to continuous production of H₂SO₄ and HNO₃ and washout of NH₃ and aerosol.