Air　quenched　slag　is　processed　by　a　fast　air　cooling　method　which　is　developed　with　the　advantages　of　recovering　heat　from　molten　slag　and　water　conservation　compared　to　the　water　quenching　method.　Air　quenched　slags　with　different　chemical　compositions　are　synthesized　in　the　lab　by　designing　three　chemical　composition　ratios:　(CaO　+　MgO)/(SiO2　+　Al2O3),　CaO/MgO　and　SiO2/Al2O3,　which　are　donated　as　CM/SA,　C/M　and　S/A,　respectively.　The　effect　of　different　chemical　compositions　on　the　phase　compositions　of　synthetic　air　quenched　slag,　the　strength　and　hydration　properties　of　slag　blends　were　investigated　by　using　various　characterization　techniques.　The　results　show　that　the　amorphous　content　of　air　quenched　slag　decreased　with　the　increasing　basicity　CM/SA　of　slag.　The　S/A　ratio　of　slag　was　the　dominant　factor　for　the　compressive　strength　of　slag　blends　at　28　days　and　negatively　correlated　with　strength.　Decreasing　the　S/A　ratio　of　slag　increased　the　reactivity　of　slag　and　its　reaction　degree　indicated　by　higher　hydration　heat　release,　lower　CH　content,　greater　chemical　combined　water　amount　and　denser　microstructure.　Moreover,　thermodynamic　modelling　revealed　that　a　higher　S/A　of　slag　leads　to　the　increase　of　C-(A)-S-H　and　AFt　contents,　whilst　decreasing　the　amounts　of　Ht,　AFm-SO4　phases　and　the　total　volume　of　hydrates.