Hydration properties of tricalcium aluminate（C3A） gypsum（CaSO4·2H2O） calcium carbonate（CaCO3） water（H2O） composite system were studied in this paper. Hydration products were tested by X ray diffraction（XRD） and differential scanning caborimetry（DSC）, and hydration process was analyzed by calorimetric method. Results show that CaCO3 slows the speed of AFt conversion to AFm and enhanced the stability of AFt. Ion of CO2-3 provided by CaCO3 leads to single sulfur aluminate transforming to single carbon aluminate, which provides the SO2-4 to promote the AFm transforming to AFt. So CaCO3 makes AFm unstable. The calorimetric results indicate that when the system containing 12.5%（by mass） CaCO3 and 12.5%（by mass） CaSO4·2H2O, hydration heat peak is promoted and the time of hydration heat peak appeared is earlier than pure C3A sample. The value of hydration heat peak and peak appearing time are between that of the pure C3A and only mixed 25% of CaCO3. Calorimetric curve expresses the characteristic with three exothermic peaks. The first exothermic peak is generated due to C3A initial hydration and the formation of ettringite（AFt）. The second exothermic peak is sharp and narrow which is due to AFt transforming to AFm and carbon aluminate. The third exothermic peak is low, wide and continuous for a relative long time, which is due to a huge amounts of carbon aluminum formation.