Monopolyethylene glycol maleate was synthesized by decompression melting method, and the synthetic process was discussed. Five factors were optimized, including alcohol and acid mole ratio, amount of catalyst, inhibitor dosage, reaction temperature and reaction time, designing L16(45) for orthogonal experiment. The best conditions were determined: alcohol acid and mole ratio was 1.0∶1, the amount of catalyst was 5%,the inhibitor dosage was 3%, the reaction temperature was 120 ℃ and the reaction time was 5 h.Under the best condionts,the esterification rate reached 95.25 %. The macromonomer copolymerized with acrylic acid, butyl acrylate and sodium allylsulfonate to produce the dispersant of coal water slurry. The coal water slurry was made by Datong coal, which viscosity was 1 550 mPa·s-1 and 2 100 mPa·s-1 after 90 min when the dispersant dosage was 1.0 % and the mass fraction of dry pulverized coal was 65%.