Natural　Hydraulic　Lime　(NHL)　has　exceptional　application　in　restoring　ancient　buildings　compared　to　Portland　cement　and　conventional　air-hardening　lime,　but　the　characteristic　of　slow　early　performance　development　limits　its　fields　of　application.　This　paper　studied　the　physical　and　mechanical　properties,　hydration　exothermic　properties,　phase　composition　and　transformation,　and　microstructure　evolution　of　slag　powder/metakaolin　composite　NHL　during　the　early　hardening　process.　The　influence　of　slag　powder/metakaolin　on　the　hardening　process　and　performance　development　of　NHL　are　systematically　evaluated.　Results　show　that　slag　powder　can　improve　the　fluidity　of　NHL-based　mortar;slag　powder/metakaolin　generates　calcium　aluminate　hydrate　(C3AH6),　calcium　carboaluminate　hydrate　(C4AĈH11)　and　calcium　silicate　hydrate　(C-S-H)　through　pozzolanic　reaction　to　promote　the　setting　and　hardening　of　NHL-based　materials　and　significantly　improve　their　compressive　and　flexural　strength.　This　study　provides　reference　for　promoting　the　application　of　pozzolanic　material　composite　NHL　in　the　restoration　of　ancient　buildings.　©　2022　Journal　of　Mining　Science　and　Technology.　All　rights　reserved.