To　clarify　the　interaction　between　chloride　ions,　limestone　powder　and　aluminum　phase,　and　their　influences　on　the　microstructure　and　chloride　ion　permeability　of　cement　pastes,　the　phase　was　analyzed　by　X-ray　diffractometer　(XRD)　and　differential　thermal　analysis.　The　micromorphology　was　observed　by　scanning　electron　microscope.　The　pore　structure　was　measured　by　mercury　intrusion　method.　The　chloride　ion　permeability　was　tested　by　RCM　methods.　On　this　basis,　effects　of　limestone　powder　with　different　amount　and　specific　surface　area　on　the　microstructure　and　chloride　ion　migration　coefficient　of　cement　pastes　under　chloride　salt　environment　were　investigated.　Test　results　show　that　with　the　increase　of　limestone　powder　amount　or　the　decrease　of　specific　surface　area,　the　chloride　ion　migration　coefficient　of　cement　pastes　increased.　When　the　content　of　limestone　powder　increased　from　0%　to　30%,　the　chloride　ion　migration　coefficient　of　cement　pastes　increased　from　7.16×10-12　m2　/s　to　22.17×10-12　m2　/s.　When　the　specific　surface　area　of　limestone　powder　increased　from　500　m2/kg　to　800　m2/kg,　the　chloride　ion　migration　coefficient　of　cement　pastes　decreased　from　22.17×10-12　m2/s　to　20.57×10-12　m2　/s.　Under　the　chloride　salt　environment,　the　XRD　diffraction　peak　of　calcium　aluminate　disappeared,　and　the　diffraction　peak　of　Friedel　’　s　salt　was　formed.　With　the　increase　of　limestone　powder　content,　the　Friedel　’　s　salt　content　first　increased　and　then　decreased.　When　the　limestone　powder　amount　was　10%,　the　Friedel　’　s　salt　content　was　the　highest,　which　was　3.70%.　When　the　specific　surface　area　of　limestone　powder　increased　from　500　m2　/kg　to　800　m2　/kg,　the　Friedel　’　s　salt　content　increased　from　3.02%　to　3.63%,　the　most　probable　pore　size　decreased　from　38.72　nm　to　36.54　nm,　and　the　porosity　decreased　from　25.63%　to　25.24%,　which　improved　the　microstructure　of　cement　pastes,　thereby　increasing　the　resistance　to　chloride　ion　permeability　of　cement　pastes.　In　the　chloride　salt　environment,　in　order　to　improve　the　resistance　to　chloride　ion　permeability　of　cement-based　materials　mixed　with　limestone　powder,　the　limestone　powder　content　should　be　less　than　20%,　and　the　specific　surface　area　of　limestone　powder　was　suggested　to　be　800　m2　/kg.　©　2022,　Central　South　University　Press.　All　rights　reserved.