Abstract: in order to explore the dispersing effect of polycarboxylate superplasticizer on low rank coal water slurry and its mechanism, the coal water slurry properties of low rank coal from three mining areas in Erdos Area were studied.The effect of the different dosage of polycarboxylate superplasticizer on concentration, viscosity, adsorption on coal surface and the influence on coal surface Zeta potential were analyzed by viscometer, ultraviolet-visible spectrophotometry and Zeta potential instrument. The results show that the polycarboxylate superplasticizer has good dispersion property, the concentration of coal water slurry of coal can increase by 20%.Before reaching the saturation dosage of the superplasticizer, the dosage of superplasticizer and slurry concentration, viscosity, adsorption and Zeta potential are highly correlated. After exceeding the saturation dosage, the slurry concentration is not increased, and the phenomenon of reverse adsorption happens. The infrared spectrum results show that polycarboxylate superplasticizer has more active points and its branch has the role of space exclusion. Its mechanism is electrostatic repulsion and steric hindrance, and dispersion is related to coal quality.