A mathematical model for an absorption of nitrogen oxides into water in packed column was developed based on the mass-transfer coefficient in packed column and the chemical reaction accompanying NOx absorption produces HNO₃ and HNO₂ in the liquid phase. The subsequent dissociation of HNO₂ in the liquid-phase results in the formation of HNO₃ and NO gas, and then this NO gas follows to be oxidized by O₂ in air. The important factors influenced on the absorption of NOx are the oxidation state of NO gas and the partial pressure of nitrogen oxides in the gas. The efficiency of NOx absorption increases with the increase of the partial pressure of NOx. The most critical value for using the model is the constant of (√(DK₃)/H)_N2O4. The selection of 11×10^-4kgㆍmol/atmㆍm²ㆍsec for(√(DK₃)/H)_N2O4 is resonable for this model.