The effects of calcined clay and limestone on early hydration, microstructure and compressive strength of low water to binder ratio (0.19) pastes under two curing systems (i.e., standard curing and steam curing) were studied. The relevant properties of the high strength cement-based materials were investigated by compressive strength test, X-ray diffraction, Hydration calorimeter and Scanning electron microscope-Electron back scattered diffraction. The experimental results show that with the decrease of calcined clay/limestone ratio (2, 1.25, 0.67 and 0.25), the compressive strength of the system first decreases and then increases. The decrease of calcined clay content makes the content of hydrated ettringite decrease. Steam curing improves the early compressive strength and hydration degree of the system as a whole, but the content of carboaluminate in the system decreases due to accelerating the hydration of early cement. Therefore, it is necessary to adopt appropriate calcined clay/limestone ratio and curing system to improve the performance of the system.