In　this　paper,　the　properties　of　cement　mortar　with　0.5　W/C　before　and　after　freeze-thaw　cycles　in　4　wt%　NaCl　solution　were　measured.　The　experiments　include　mass　loss,　X-CT　scanning　and　axial　compression　full　curve.　Results　showed　that　cement　mortar　damage　under　freeze-thaw　cycle　was　a　layer-by-layer　peeling　process　from　exterior　to　interior.　As　the　freeze-thaw　cycles　proceeded,　the　initial　mass　loss　rate　of　mortar　slowly　increased　and　then　the　rate　rapidly　increased,　and　a　mass　loss　prediction　equation　was　proposed.　Using　X-ray　CT　scanning　and　3D　reconstruction　technology,　a　method　for　the　evaluation　of　the　internal　damage　rule　of　cement　mortar　under　freeze-thaw　cycles　was　proposed.　The　porosity　change　of　sample　before　and　after　freeze-thaw　cycles　was　calculated　by　X-ray　CT　scanning　technology.　As　the　number　of　freeze-thaw　cycles　increased,　the　porosity　increment　of　the　samples　increased　approximately　linearly.　The　peak　compressive　stress,　initial　elasticity　modulus　and　residual　strength　of　cement　mortar　caused　by　freeze-thaw　cycles　reduced　gradually,　and　with　the　increase　in　cycling　number,　the　downward　trend　became　more　obvious.　Based　on　mass　loss　and　the　change　of　internal　overall　porosity　of　mortar,　an　elastic　modulus　damage　model　of　cement　mortar　was　established　which　is　in　good　agreement　with　the　experimental　results.　(C)　2018　Elsevier　Ltd.　All　rights　reserved.