To strengthen the CO2 absorption, Ca(OH)2 was introduced into the urea-NaClO2 absorbent. CO2 was abundantly absorbed in the early stage of absorption. When Ca(OH)2 content was 2 wt%, CO2 kept ∼90% conversion for more than 30 min. SO2 conversion remained above 95%, while the conversion of NO was suppressed in the early stage of absorption, and the suppressing time increased with a higher Ca(OH)2 content. The oxidizing ability of NaClO2 is inhibited at relatively high OH− concentrations. The addition of Ca(OH)2 increased the OH− concentration of the solution, hence inhibiting the NO oxidation. But the NOx conversion in the later stage of absorption was increased by up to 10%. The absorption of NO oxidizing products (e.g., NO2) may be enhanced by Ca(OH)2. The absorbed CO2 showed linear relationship with added Ca(OH)2 (Fig. 3). Theoretically, 1 mol Ca(OH)2 could absorb 1 mol CO2 (CO2 + Ca(OH)2 → CaCO3 + H2O), leading to a slope of 1 in the fitting line. Nevertheless, the slope of the fitting line from experimental results was 0.566 (R2 = 0.990), indicating that there was part of the Ca(OH)2 reacted with SO2 and the Ca(OH)2 may not be completely reacted. The pH values of the absorbents before and after reactions were measured. When 0.068 mol (0.5 wt.%) and 0.135 mol (1.0 wt.%) Ca(OH)2 were added, the pH finally dropped to ∼7, similar with the situation without urea and Ca(OH)2 addition, indicating that the dissolved urea and Ca(OH)2 in the absorbent liquid was almost reacted. When the addition amount was 0.270 mol (2.0 wt.%), the pH dropped to ∼10, close to the initial pH of absorbent without Ca(OH)2, indicating that the liquid phase Ca(OH)2 reached exhaustion and the urea-NaClO2 started to be consumed at this time.