The early hydration characteristics of the system C3S-C3A-C4AF according to the clinker composition variations, in order to establish the mutual interactionof clinker minerals during the portland cement hydration, have been studied. The early hydration rate of C3S was greatly effected by the change of C3S/C3A ratio. The lower the C3S/C3A ratio was, the faster the apex reaching time and the rate of heat liberation of the 2nd exothermic peak originating from the formation of Ca(OH)2 were. The effect of C3S/C3A ration on the amounts of Ca(OH)2 formation was decreased, in process of hydration time, but the effect of C3S content was increased.