Abstract: A series of allyl polyethylene glycol polycarboxylate dispersants was prepared with four different relative molecular mass allyl alcohol polyoxyethylene ( APEG) and methy| acrylate ( MAA) as monomer, K2 S 208 as initiator and hydroquinone as inhibitor by one step synthesis method. The copolymer structures were ch aracterized by infrared spectrum and the relative molecular mass and its distribution was analyzed by gel permeation chromatography. The influences were explored of the different side chain length of dispersants on the slurry performance and the apparent viscosity of Binchang coal water slurry. Based on the performance results, the synthesis optimized conditions of copolymer was obtained. The mass ratio of methyl acrylate and allyl alcohol polyoxyethylene was 1 : 1, dosage of the initiator was 4% of the monomer quantity, the polymerization temperature was 80。C and the reaction keeping time was 5 h. The results showed that polycarboxylic acid dispersant with t he side chain length of 27 had better dispersing and stabilizing effect to Binchang coal.