Multiple　additives　are　usually　required　to　achieve　better　constructability　for　building　gypsumbased　materials.　In　this　work,　ternary　contour　was　designed　to　determine　the　optimal　proportions　of　Ca(OH)2　(CH),　PCEs　and　citric　acid　(CA)　by　comprehensive　considerations　of　water　requirement,　setting　time,　fluidity,　strength,　temperature,　hydration　products　and　microstructural　characteristics.　The　effects　of　different　additives　on　water　requirement,　setting　time,　fluidity,　compressive　strength,　hydration　products　and　microstructure　were　comprehensively　investigated,　and　the　associated　mechanisms　were　revealed　by　X-ray　diffraction　(XRD),　and　scanning　electron　microscopy　(SEM)　tests.　The　results　demonstrate　the　synergistic　impact　of　PCEs　and　CH　on　decrease　of　the　water　demand　and　enhancement　of　fluidity　and　compressive　strength.　The　incorporation　of　CH　led　to　rapid　setting,　but　compensated　the　strength　reduction　brought　by　CA.　The　optimum　additives　for　building　gypsum　were　obtained　with　a　ternary　mixture　containing　0.1-0.9　%　CH,　0.6-1.4　%　PCEs　and　0-0.08　%　CA,　since　it　guaranteed　a　longer　setting　time,　lower　water　requirement　and　higher　strength.　The　present　work　paves　the　way　to　optimize　or　predict　the　early　hydration　and　mechanical　properties　of　building　gypsum　in　both　technical　and　economic　aspects　by　adjusting　the　proportions　of　the　three　additives.