To achieve simultaneous removal of NOx and SO2 in flue gas, an effective technology combined with ozone oxidation was explored in this paper. The simulated flue gas was initially oxidized by ozone (O-3), turning NO into NO2 or N2O5, and then absorbed by alkaline slurries to achieve simultaneous removal of NOx and SO2. It was found that the MgO slurry was a suitable absorbent for the simultaneous removal of NOx and SO2. The operating parameters, such as the pH of the liquid phase, initial SO2 concentration, and MgO concentration, were investigated for the NO2 removal efficiency of the MgO slurry, where the optimal NO2 removal efficiency (at ca. 75%) was Obtained with the pH value at 6.5 and the MgO Concentration at 0.02 mol/L. In the case of N2O5, the absorption efficiency of the MgO slurry was maintained at a high level because of the rapid reaction between N2O5 and H2O. Furthermore, it was noted that the absorption efficiency of SO2 could be at a high level (i.e., approaching 100%) when the pH Of the MgO slurry was above 4. Finally, the simultaneous removal mechanism and the reaction pathways were discussed on the baths of the experimental results.