Phosphogypsum　slag-based　composite　cementitious　materials　were　prepared　by　using　phosphogypsum　and　slag　powder　as　the　main　raw　materials,　adding　quicklime,　lithium　slag,　steel　slag　and　other　admixtures,　and　adding　NaOH,　NaHCO3　and　triethanolamine　(TEA).　The　effects　of　different　admixtures　on　the　fluidity,　setting　time　and　compressive　strength　of　the　composite　cementitious　materials　were　studied.　Finally,　XRD,　MIP,　TG-DTG,　and　SEM　microscopic　tests　were　used　to　analyze　the　reasons　for　the　performance　changes　caused　by　the　admixture　from　the　aspects　of　phase　composition,　pore　distribution,　and　hydration　product　morphology.　The　results　show　that　the　addition　of　NaOH,　NaHCO3　and　TEA　reduces　the　fluidity　and　strength　of　the　material　and　improves　the　setting　time.　The　paste　with　1　%　NaOH　and　0.03　%　TEA　can　balance　the　working　performance　and　mechanical　properties.