The hydration properties of compound cementitious materials(CCM) under steam curing condition quite differ from those under standard curing condition.The effects of steam curing condition and composition of cementing materials on hydration degree and hydration products of CCM with high volume of fly ash and ground granulated blast furnace slag were investigated.The non-evaporable water and calcium hydroxide(CH) content method were used to determine the hydration degree of these cementitious materials,and X-ray diffraction analysis was used to determine the hydration products of CCM.The results show that the steam curing accelerates the CCM hydration,especially at steam curing period.The CH content,as well as the non-evaporable water content can be used to evaluate the dydration degree of cement paste.However,it is necessary to consider the CH consumption due to pozzolanic reaction of mineral admixtures when using CH content to determine the hydration degree of CCM.The steam curing condition has no effect on the variety of the hydration products but on their amount and improves pozzolanic activity of mineral admixtures.