This paper focused on the preparation of a dispersant which takes rosin as raw material, then adds maleic anhydride and finally applies diethanolameine to modify to get the Maleopimaric acid diethanolamine dispersant that was used in coal water slurry (CWS). This dispersant has a lot amount of alcohol amide structures which can make water moisten the coal surface rapidly. Studies on dispersant’s effects on rheological behaviour of CWS with different concentration, pH and shear rates, Zeta potential for different concentration are carried out to analyze the interaction of dispersants and the surface of coal particles. Dispersants make viscosity of CWS lower because of homogeneous moistening of coal particles through dispersants’ hydrophobic groups connecting to the surface of coal and their hydrophilic groups connecting to water molecular, breaking coal particles gathering and increasing stability of CWS effectively.