Abstract: The zeta-potential on particle surface has a great bearing on settling characteristics of solid particles in coal slurry water, and the pH value of the slurry water can directly affect the surface electric property of particles and the existence form of coagulant/flocculant in slurry water. Measurements of surface potential of solid particles in slurry water are made using microelectrophoresis apparatus after the pH value of the water is adjusted with NaOH and HCl. Test shows that at a pH value of 2.7, the zeta-potential is equal to zero, with an isoelectric point of 2.7.