In this work, effects of limestone powder on hydration of $C_3A-CaSO_4{cdot}2H_2O$ system was discussed based on the XRD Quantitative analysis, and the possibility of Delayed Ettringite Formation was also discussed. The early hydration of $C_3A$ was delayed by addition of $CaCO_3$ powder. The delay effect was enhanced by increasing of $CaCO_3$ content and finer powder of $CaCO_3$ addition. After consumption of $CaSO_4{cdot}2H_2O$, the reaction of $CaCO_3$ is started. Delayed Ettringite Formation would take place because monosulfoaluminate is not stable in presence of $CaCO_3$. In order to prevent the delayed ettringite formation in $C_3A-CaSO_4{cdot}2H_2O-CaCO_3$ system, the reduction of monosulfoaluminate formation is important. Therefore, by increasing the amount of $CaCO_3$ addition and finer $CaCO_3$ powder addition, the delayed ettringite formation can be prevented.