Concrete　cracking　is　a　major　cause　affecting　the　durability　and　applicability　of　concrete;　it　draws　increasing　attention　from　researchers　in　the　field　of　civil　engineering.　However,　previous　studies　of　early　micro-cracks　are　insufficient.　The　presence　of　early　micro-cracks　is　the　basis　of　macroscopic　cracks.　Therefore,　a　calculation　method　of　internal　stress　within　cement　paste　caused　by　core　restricted　shrinkage　under　the　core　restricted　condition　of　rigid　body　was　studied,　and　a　mechanical　model　of　internal　stress　was　established.　Based　on　the　model,　the　factors　that　affect　internal　stress　within　cement　paste　were　further　analyzed,　and　the　law　of　strain　variation　of　cement　paste　under　the　rigid　elastic　body　confinement　was　discussed.　The　results　show　practical　significance　in　the　control　of　crack　development　and　in　the　improvement　of　concrete　durability.