The polycarboxylate superplasticizer(PC) was synthesized with methoxy polyethylene glycol methacrylate, methacrylic acid, sodium methyl acryl sulfonate as monomers, using ammonium persulfate (APS) as initiator. The effect of the mole ratio of different monomers on dispersing properties was analyzed. Results show that dosage of monomers and initiator impact molecular weight and dispersing properties of PC greatly; When mole ratio of MAS, MAA and PMA45 is 0.5:3.75:1, dosage of APS is 0.4%, the product of PC has best properties, with 45.09 ml?g-1 of inherent viscosity; when used in cement system with W/C ratio of 0.25 and dosage of 0.2%, the initial fluidity is 269 mm and 281 mm 30 min later.