Fly ash (FA)is a widely used supplementrary cementitious material.However, the pozzolanic activity of FA is always so limited that physical or chemical methodology can be used to improve its hydration activity.In this study, FA was pre-activated with NaOH using fluidized bed reactor-vapor deposition (FBR-VD).Comparison between this pre-activating method and the traditional chemical activation was conducted.The compressive strength of cement paste was tested.The hydration degrees of cement clinker and FA in the cement paste were analyzed.And the microscopic images of the pre-activated FA and hydrated paste were investigated by SEM.Results figure out that the compressive strength of the sample with pre-activated FA is higher than that with directly dosed chemical activator when the NaOH dosage rate is 0.1% by mass of the cementitious material.The hydration degree of cement is also increased at this NaOH rate.The hydration degree of FA, nevertheless, is raised more by FBR-VD when the NaOH dosage rate increases fiom 0.1% to 0.5%.NaOH can recrystallize on the surface of FA beads, reacting with them to form some activated points.The activated points will cause the cements hydrating nearby and make the FA stuck to the cement matrix more tightly.