In　this　paper,　the　strength　development　of　a　pure　steel　slag　(SS)　system　with　various　concentrations　of　N,N,N　＇,N　＇-Tetrakis-(2-hydroxyethyl)　ethylenediamine　(THEED)　was　investigated.　The　hydration　kinetics,　pore　structure　and　microstructure　of　SS　pastes　with　and　without　THEED　were　characterized　to　underscore　the　working　mechanism　of　THEED.　Results　show　that　THEED　additions　significantly　increase　the　3,　7　and　28　days　compressive　strength　of　hardened　SS　pastes.　The　enhancement　effect　increases　with　the　dosage　of　THEED.　At　a　concentration　of　2000　ppm,　THEED　increased　the　compressive　strength　by　733%,　665%,　and　545%　at　3,　7　and　28　days,　respectively.　It　is　confirmed　that　THEED　additions　improve　the　hydration　degree　of　SS　by　accelerating　hydration　of　the　aluminum　phase　(C3A,　PDF-38-1429;　C12A7,　PDF-48-1882)　and　C2F,(　PDF　38-0408)　to　generate　Mc　(PDF-41-0219)　and　Pa　(PDF-30-0222)　in　the　presence　of　CaCO3.　Also,　the　hydration　degree　of　silicates　is　increased　by　THEED.　In　this　way,　THEED　additions　refine　the　pore　structure　of　hardened　SS　paste　by　increasing　the　pore　volume　with　a　diameter　below　300　nm　to　achieve　enhancement.　The　chelating　effect　of　THEED　results　in　promoting　dissolution　of　SS,　which　provides　the　driving　force　for　accelerating　SS　hydration.