imestone powder (LP) actually has hydration activity and can reacts with aluminate minerals, such as C₃A in Portland cement, and CA and CA₂ in aluminate cement (AC). The hydration product is calcium carboaluminate hydrate. In this paper, in order to study the hydration reaction, composite systems, which consist of limestone powder and aluminate cement, were analyzed by micro calorimeter, strength test and XRD. The results show that, LP could accelerate the hydration process of the system, and lead to a shorter induction period, an earlier and lower hydration heat peak in the hydration of aluminate cement. The more LP in the composite system, the faster the early hydration, but the lower the hydration heat of the composite system. 20% replacement of limestone powder is the most reactive and contributes significantly to the strength of the composite system. The more limestone powder in the composite system, the less hydration products of the aluminate cement. When the limestone powder content is 20%~40%, the XRD peak of calcium carboaluminate hydrate is relatively obvious. Accordingly, there is a optimal range of AC:LP in the composite system. It is concluded that a significant hydration reaction occurs between limestone powder and aluminate cement. The composite of limestone powder and aluminate cement is expected to produce a new type of cementitious material.