Based　on　the　experiment,　a　micro-mechanical　model　is　developed　to　investigate　the　evolution　of　the　microstructure　and　effective　properties　of　the　cement　paste　in　the　hydration　of　the　cement,　assuming　that　the　cement　paste　composite　consists　of　anhydrous　cement　particles,　cement　gel　and　pores　in　the　model.　The　cement　particles　have　a　periodic　distribution　and　are　wrapped　by　the　cement　gel.　The　instantaneous　Young＇s　modulus　and　Poisson　ratio　of　the　cement　paste　are　calculated　by　the　direct　average　method　and　two-scale　expansion　method.　A　comparison　between　the　numerical　results　and　experimental　data　shows　that　this　model　can　simulate　the　evolution　of　the　micro-structure　and　properties　of　the　cement　in　the　hydration.　The　present　method　can　be　extended　to　model　property　evolution　of　other　hydrous　media.