This study focuses on the blended cement containing ground granulated blast furnace slag (GGBFS) and waste clay brick (CBP), with 30% and 50% Portland cement contents. The compressive strength, hydration kinetics, hydration products and microstructure of blended cement up to 365 d were investigated to explore GGBFS and CBP interaction in the blended cement. The results show that both GGBFS and CBP reduce the hydration heat of blended cement, but the GGBFS will accelerate the C3A hydration more significantly due to consuming more sulfate than CBP. The improvement effect of GGBFS on compressive strength mainly occurs before 90 d, while the reaction of CBP continues to improve the compressive strength after its drastic reduction at early age. The X-ray diffraction and thermogravimetry results prove that the blended cement containing both GGBFS and CBP shows a high hydration degree at early age and will continue to hydrate. Furthermore, the chemically bound water content and porosity in blended cement containing both GGBFS and CBP at 365 d are almost the same as those in Portland cement.