Abstract Coal water slurry (CWS), a highly-loaded suspension of coal in water, is regarded as one of the most important alternatives for fuel oil. Generally, additives are required for the preparation of CWS, of which polycarboxylate (PC) is the most promising and applicable one. PC was synthesized by free radical polymerization of acrylic acid, acrylamide and macro-monomer, and was further characterized by FTIR and 1H NMR. The performance of PC as additives for CWS was evaluated and the dispersion mechanism was also studied. Results showed that the additive was a polymer with comblike branched chains modified by COOH and CONH2 groups. The CWS based on bituminous coal with PC additive displayed excellent fluidity and stability (i.e. the apparent viscosity and penetration ratio of CWS with 65 wt% coal and 0.4 wt% additive were 305 mPa.s and 79.8%, respectively) for the most suitable coal type. The properties of the CWS can be further enhanced by using simultaneously PC and aliphatic additives because of the steric hindrance effect and electrostatic force.