Abstract: The effect of metal salts on the physical structure of CaCO3 was studied by using sodium carbonate as the additive and PoreMaster-60 mercury porosimeter. The investigation shows that the BET surface area and porosity increase and the pore distribution of CaCO3 is optimized, especially, the effect is more evident as the ionic ratio of calcium to sodium is equal to fifteen. At the same time, the characteristics of SO2 release from coal combustion in the atmosphere of O2/CO2 with adding CaCO3 was compared to that with adding modified CaCO3 by using ZCS-1 intelligent sulfur analyzer, and the ash melting point test and XRD analysis were carried out with the combustion products. The results show that without aggravating slagging, the SO2 retention is enhanced by modifying CaCO3, and the best sulfur fixation efficiency is reached at 1 000 ℃.