Abstract: Based on the experiment , a micro-mechanical model is developed to investigate the evolution of themicrost ructure and effective properties of the cement paste in the hydration of the cement , assuming that the cementpaste composite consist s of anhydrous cement particles , cement gel and pores in the model. The cement particleshave a periodic dist ribution and are wrapped by the cement gel. The instantaneous Youngps modulus and Poissonratio of the cement paste are calculated by the direct average method and two-scale expansion method. A comparisonbetween the numerical results and experimental data shows that this model can simulate the evolution of the microst ructure and properties of the cement in the hydration. The present method can be extended to model propertyevolution of other hydrous media.