Abstract: The effect of temperature on SO2/SO3 conversion rate under the action of SCR catalyst was studied on a self-developed experimental setup, in which case, the absorption capability of Ca-based and Mg-based sorbents to SO3 was investigated, and simultaneously the samples were analyzed using scanning electron microscopy before and after adsorption experiment, so as to analyze the factors influencing the SO3 adsorption by Ca-based and Mg-based sorbents and the removal mechanism. Results show that the SO2/SO3 conversion rate increases with rising reaction temperature, and the increasing tendency slows down when the temperature gets up to 300 ℃. The conversion rate has a good linear relationship with the temperature in the reaction scope. The adsorption capability of the four sorbents tested to SO3 are ranked from high to low as follows: Mg(OH)2, Ca(OH)2, MgO and CaO.