In the article, experiment study was made on the desulfurization ability of hydrolime based on thermal balance. The result shows: though impurities in different hydrolimes used as absorbent can increase the activation, CaO exerts the fatal importance to the desulfurization efficiency. The law for absorbent absorbing CO2 is different from that for SO2 . With the increase of the water/solid weights rate, the absorbed quantity of CO2 first increases and then maintains unchanged or even decreases. However, as regards SO2, the absorbed quantity increases along with the increasing of the water/solid weights rate which makes great, affect on the desulfurization. When there is CO2 in the flue gas, the conversion increases and the desulfurization efficienxy decreases.