The cement sample was sieved into three grades i.e. S(030μm), M(3060μm) and L(60160μm). The aim of this work was to study the early hydration performance of the three cement samples by analyzing the particle size distribution, mineral composition, early hydration rates of the three cement samples, and the composition and profile of their early hydrates. Results show that the content of main mineral phases vary for the three cement samples. The content of C3S is in order of L>M>S, and the content of C2S, C3A and CaSO4·2H2O are all in order of S>M>L. The hydration rate of cement sample S is much faster than cement samples M and L. At early hydration period, large numbers of needle bar AFt are formed on the surface of cement sample S, while the hydration products of cement samples M and L are mainly gelatinous AFm and lamellar C4AH13.