Polycarboxylate terpolymer superplasticizer of MAPEG-HEA-SMAS was sunthesized by copolymerization with esterification intermediate（MAPEG），hydroxyethyl acrylate（HEA）and sodium methallyl sulfonate（SMAS）as main raw materials. The influence of molar ratio of monomer，dosage of initiator，reaction temperature and reaction time on the copolymerization were investigated. The structure was characterized by IR. Relative molecule mass and its distribution of superplasticizer is measured by GPC, and the microstructure of cement is characterized by SEM. The results show that when the molar ratio of MAPEG to MA to SMAS is 1.0:1.0:1.5，the polymerization reaction temperature is 88℃,the polymerization reaction time was 7.5h, the dosage of initiator is 3.5% of total monomer mass and the relative molecule of PEG mass is 1000,the superplasticizer prepared under this condition would exhibit good performance.The original fluidity of cement grout can reach 308mm with 0.45% percentage mass content of this superplasticizer(mass fraction).GPC shows that the mean molecular weightMn)and polydispersity Mw/Mn of the superplasticizer is 7752 and 2.091.SEM shows the amount of macropors of cement added with the polymerization reduce, and the crystals grow more dense.