As one of the typical solid-wastes, FGD gypsum usually occupies land and causes resource waste and environmental pollution. Its high content of CaSO4 center dot 2H(2)O shows highly potential in synthesizing CaCO3 by incorporating CO2. Nevertheless, the impurities in FGD gypsum have significant effects on polymorph of CaCO3 and the formation mechanism of CaCO3 polymorph during FGD gypsum carbonation was still unclear. Here, we selected CaSO4 center dot 2H(2)O as model to explore the effects of impurities of muscovite and dolomite in FGD gypsum on poly morph of CaCO3 during carbonation. Results showed that the carbonation products of FGD gypsum are a mixture of vaterite C60%) and calcite C40%), while only pure vaterite was obtained in CaSO4 center dot 2H(2)O carbonation reaction. Muscovite has negligible effects on obtaining pure vaterite during CaSO4 center dot 2H(2)O carbonation. Interestingly, the content of calcite increases to the maximum value (-27%) at 1.0 wt% dolomite and then decreases with the increment of dolomite in CaSO4 center dot 2H(2)O carbonation reaction. Correspondingly, vaterite declines first and then increases. Mechanism study shows that hydrophilicity and negative surface charge of dolomite might be the key factors to selectively form calcite during the carbonation of FGD gypsum. These findings might contribute to further utilization of FGD gypsum.