The　molecular　weight　and　molecular　weight　distribution　(MWD)　of　polycarboxylate　superplasticizer　(PCE)　was　measured　by　gel　permeation　chromatograph　(GPC)　which　combined　three　different　detectors,　namely　refractive　index　detector　(RI),　laser　light　scattering　detector　(LS)　and　viscosity　detector　(VIS).　By　conducting　numerous　experiments,　what　the　different　peak　stand　for　in　the　chromatogram　was　verified　and　the　best　sample　concentration　range　in　the　GPC　experiment　was　also　determined.　Besides,　based　on　the　analysis　to　the　RI　chromatogram,　the　theory　on　using　peak　area　ratio　to　denote　concentration　ratio　was　put　forward.　What＇s　more,　the　calculation　of　macromonomer　reaction　ratio　using　the　peak　area　in　the　RI　chromatogram　was　introduced.