A new intermediate macromonomer for polycarboxylate type superplasticizers was prepared by esterification of itaconic acid and polyethylene glycol. The conditions of the esterification were investigated by orthogonal experiment. The optimum conditions were obtained as follows: the molar ratio of itaconic acid to polyethylene glycol is 1:1.1; the amount of catalyst is 4% according to the mass of polyethylene glycol; the reaction temperature is 100℃; the reaction time is 6h; the amount of water-carrying agent is 30% according to the mass of polyethylene glycol and the amount of polymerization inhibitor is 2% according to the mass of itaconic acid. Under the optimum conditions, the percentage of esterification is as high as 98.3%. The macromonomer was characterized by FTIR and 1H-NMR. The result indicated that the macromonomer, the itaconic acid polyethylene glycol ester, was obtained.