The hydration process, activity and microstructure of composite cement-based materials containing fly ash(FA)and flue gas desulphurization gypsum(FGD)were investigated by using DTA-TG, XRD, SEM, hydration shrinkage and compressive strength tests. And then the hydration kinetics of composite cement-based materials was discussed and summarized. It is shown that the ettringite(AFt)DTA endothermic peak of the harden cement paste containing FA and FGD is stronger than that of the reference specimen. The secondary hydration effect of hardened FA-FGD cement paste is more obvious under the effects of mutually active excitation and the added activators. The results of SEM and XRD indicate that the AFt in harden cement paste is significantly found and the surface of FA particle is eroded, further illustrating that the early activity of composite cement-based materials is effectively motivated, and ensuring the comprehensive properties of hardened composite cement-based materials. On the other hand, the test results of microscopic test were confirmed by the hydration shrinkage and compressive strength tests. Therefore, this research and application of FA-FGD composite cement-based materials can consume a lot of industrial wastes discharged from the power plant. It is a kind of “green” building material.