The influence of different amount of SiO2 powder on the mechanical properties of cement-quartz composite cementitious material was discussed through the measurement of the compressive strength of the paste with the water/binder ratio of 0.5 and 0.2 where the SiO2 powder with different proportion to replace the Portland cement(PC). The compressive strength test shows that adding SiO2 powder to the concrete with low water-binder ratio can reduce the use of cement.