Polymaleic acid was synthesized in water phase by adopting maleic acid as raw material and H ₂O ₂ as initiator. Then a novel polycarboxylate superplasticizer of PMA-AA-AMPS was synthesized by using polymaleic acid (PMA), acrylic acid (AA) and 2-acrylamido-2 methyl-propane sulfonic acid as raw materials, ammonium persulfate as initiator in aqueous media. Additionally, the polymerization conditions were optimized. The results indicate that the copolymer can be prepared under such optimum conditions, i.e., 6∶3∶1.2 molar ratio of MA，AA and AMPS，8% of the mass fraction of ammonium persulfate，6% of the mass fraction of formate sodium, 85 ℃ of the polymerization temperature and 3 h of the reaction time. The characterization results of FTIR indicate that the prepared terpolymer contains functional anionic groups such as carboxyl，hydroxyl，sulphonate and amido groups. The number average molecular weight of the PMAAA from GPC is 5 743 g/mol occupying 81.36% of the whole mass fraction.