Based on the serious pelitization of coal preparation plant, slime water with difficult sedimentation, precipitation effect of flocculant addition alone is not obvious, combining with strong negative charge of particles, slime water particles settling down was analyzed under different conditions, the result showed that the increased drug could effectively accelerate the sedimentation rate; Weak acid environment can not enhance the settlement effect; Ca2+ and Mg2+ have obvious effects on the sedimentation of slime water. The treatment of slime water with polyacrylamide flocculant alone has little effect.