Cement　based　materials　are　especially　vulnerable　to　serious　temperature　changes　in　saline　land　or　marine　environments,　resulting　in　the　degradation　of　structures　and　properties.　As　the　main　binding　components　in　cement　based　materials,　the　investigation　of　the　C−S−H　gel　structure　and　water　molecules　behaviors　enabled　the　detail　damage　mechanism　of　cement-based　material　under　different　temperatures.　In　this　study,　C−S−H　gel　models　were　successfully　constructed　with　the　final　chemical　formula　of　(CaO)1.65(SiO2)(H2O)1.79.　Systematical　research　works　were　performed　on　the　structures　and　properties　of　both　C−S−H　gel　and　water　molecules　in　different　local　environments　by　molecular　dynamics　(MD)　under　temperatures　ranging　from　100　K　to　500　K.　Subsequently,　the　time　correlation　function　(TCF)　and　mean　square　displacement　(MSD)　methods　were　introduced　to　explore　the　dynamic　properties　of　various　chemical　bonds.　The　volume　expansion　of　C−S−H　gel　under　higher　temperatures　resulted　from　stretched　bond　length　between　silicon　atoms　and　oxygen　atoms,　and　variation　of　corresponding　bond　angles.　In　addition,　higher　temperatures　promoted　the　prolonged　hydrogen　bond　length,　thus　reduced　the　number　of　hydrogen　bond.　Moreover,　the　polarization　of　water　molecules　was　weakened　gradually　under　higher　temperatures,　but　water　molecules’　orientation　fluctuated　obviously　along　the　out　of　plane　directions　of　interlayer　region.　Additionally,　MSD　results　revealed　that　water　molecules　showed　temperature　dependent　diffusion　behaviors　in　different　chemical　environments.　©　2020　Elsevier　Ltd