Abstract: The preparation process of calcium carbonate by carbonation of CO2 and calcium ion in weak-acid medium was studied. The affecting factors such as concentration of calcium acetate，pressure of CO2，reaction temperature，time of aging and reaction time on the preparation of precipitated calcium carbonate were discussed. The optimum reaction conditions were as follows：concentration of calcium acetate 17%，carbon dioxide pressure 2.5 MPa，reaction temperature 95 ℃，reaction time 30 minutes，and ageing time 5 hours. The yield of calcium carbonate was about 20.6%. The calcium carbonate particles had good dispersivity and the volumetric mean size was about 1.4 μm. This process provides the basic experimental data for comprehensive treatment of CO2 and calcium containing slag to produce calcium carbonate.