Hydration characteristic and microstructures of water entrained cement paste with water-cement ratio (w/c) of 0.30 cured under saturated condition were studied. Degree of hydration was quantified by loss on ignition (LOI) measurements and BSE imaging. Volume of capillary pore of the hydrated paste was evaluated by using scanning electron microscopy. Degree of hydration of internally cured cement paste under saturated condition is higher than that of control paste without water entrained. A reduction of volume of capillary pore is obtained for the promotion of cement hydration. Quantity of entrained water is a time dependent function at early age in the presence of continuous external water supplying. A model was proposed for evaluation degree of hydration of cement under a combination of internal curing and saturated curing, based on equivalent w/c. Experimental results indicate that internal curing can efficiently accelerate early age hydration of cement and that only 50% of theoretical entrained water is needed for mitigation chemical shrinkage and for achieving maximum degree of hydration of cement paste with low water-cement ratio.