In　order　to　study　the　shrinkage　characteristics　of　cement　paste,　environmental　scanning　electron　microscope　was　used　to　observe　the　microstructure　shrinkage　of　cement　paste　and　cement　mortar　under　different　humidity.　The　results　showed　that　:　with　the　relative　humidity　decreased　from　80%　to　10%,　the　shrinkage　cracking　of　paste　microstructure　appeared　in　different　degree　and　increased　continuously,also　the　regression　analysis　showed　the　relative　humidity　and　shrinkage　was　conical　relationship.