Coal washing waste water is weakly alkaline colloidal system, its main features are: 1, the particle surface with a strong negative charge, showing a particle surface coal washing wastewater negatively charged colloidal system; 2, SS concentration and COD concentration are high; 3, high levels of fine particles; 4, viscosity; 5, mud larger than resistance, poor filtration performance. Coal washing wastewater suspended particles long home unsinkable, difficult to handle. The fundamental reason is suspended particles with a strong negative charge makes washing water and colloidal dispersion was mainly reflected in the potential of the colloid. Because one can generate a strong electrostatic repulsion between the negatively charged particles with strong potential and the electrostatic repulsion between particles, the higher the greater, more stable particles, 2, due to the Brownian motion of particles between micelles leaving the colloidal stability of the electrostatic repulsion has 3 charged particles can attract polar water molecules to form a layer around it to prevent hydrate film between particles in contact with each other. Hydration film thickness depends on the thickness of the diffusion layer and the diffusion layer thickness also affect potential. If the rubber membrane potential to eliminate or weaken the hydration disappeared or weakened. Therefore, coal washing wastewater treatment to reduce the potential damage first colloidal stability then take other measures to strengthen the cohesion effect.