| Based on the systematic research of the chemical composition,structure and basic physicochemical properties, the main object was flue gas desulfurization gypsum in this paper. Comparing with the natural gypsum, the influence of the FGD gypsum as the retarder on the correlative physical properties of Portland cement was especially discussed, and its optimal content range was explored. According to the composition and characteristics of the FGD gypsum, the influence of the different water ratio of the FGD gypsums and the content of calcium sulfite on the hydration and properties were studied. Besides, the mutual adaptability between the FGD gypsums and TIPA grind aid was discussed. The composition and structural characteristics of the FGD gypsums, cements and the hydration samples were analysed by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM), Multi-function pH meter etc. The rules of the correlated reaction and the mechanism were discussed.The result showed that the composition of the FGD gypsums was more complex than that of natural gypsum because of the impurities such as CaCO3 and CaSO3·0.5H2O it contained, large numbers of flaw lied in the CaSO4·2H2O crystal structure and the activity was relatively high. At the same content of SO3, the FGD gypsums had more obvious retarding activities than natural gypsum, and its mechanical enhancement effect on cement was superior to the latter. Their optimal content ranges were broadly similar and the optimum mix amount was 2.5% for SO3. Excessive water ratio of the FGD gypsums was obviously bad to cement properties without drying processes. When the water content of the FGD gypsums was over 15%, the strength of cement reduced obviously because of hydration reactions between plethoric attached-water and fine clinker during grinding process in advance which made the strength lost partly beforehand. So when the water ratio in the FGD gypsums was too much, the drying steps should be taken. Tri-isopropanolamine grind aid had not only good dispersion, but its polar molecule could stimulate the chemical activity of solid-phase particles, improve the hydration of cement, and make the structure of cement pastes more perfect.It and the FGD gypsum with complementary effect, could further improve physical and mechanical properties.Due to small dissolution rate of CaSO3·0.5H2O in water, it could not effectively adjust the fast hydration of tricalcium aluminate mineral, and had little effect to the hydration of cement. In the late stage, the hydration products was mainly AFm, which could expand the volume of cement pastes, because it could continue to generate the AFm. When the content of SO3 was 2.5% in cement system, together with CaSO3·0.5H2O and CaSO4·2H2O,the proportion of CaSO3·0.5H2O should be adjusted to 0～57.1% of sulfate. The setting characteristics of cement pastes sample was in normal range, the difference of the strength development in early stage was not significant. The inherent cause was still the low dissolving rate of CaSO3·0.5H2O, it could continue to create the Afm after the hardening of cement paste, which could cause harmful stress to reduce the late strength.
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