Abstract: In this paper, the thermal dilation coefficient (TDC) of cement is studied. The experimental results show that cement fineness has prominent effect on the TDC of cement paste for 28 day age, and the TDC of cement paste rises with the increase of cement fineness. So the linear formula on the relation between TDC and fineness is established. With adding fly ash, the TDC of cement paste or mortar is decreased obviously. When the amount of fly ash exceeds 30%, the TDC of cement mortar has a little change. The TDC of cement paste or mortar increases with mixing slag powder. But by mixing fly ash and slag powder, the change trend of the TDC of cement paste is not significant.