Copolymerization process of methyl allyl polyethylene glycols ether （HPEG） and acrylic acid （AA） were studied by gel permeation chromatography. The effects of monomer molar ratio and synthesis process on HPEG conversion rate, the copolymer composition and properties of synthetic polyether type high performance water reducer were investigated. The results show that the conversion rate of HPEG is increased and dispersal property of the synthetic water reducer firstly increases and then decreases with the increase of monomer molar ratio of AA to HPEG. The ratio of AA to HPEG is low in the initial stage and high in the late stage of polymerization when the addition of AA is keeping dropping at a constant speed. When changing the feed methods of AA, the synthetic water reducer receive a performance improvement with the increase in the dosage of AA in the initial of polymerization and the best dispersing property can be obtained by adding 20%（by mass）AA at the beginning and dropping the rest of AA monomer at a steady speed when the monomer mole ratio of AA to HPEG is 4∶1.