In order to reduce the amount of slime water, the particle size of slime in the primary settling tank, regulating tank and clarifier were analyzed, and the effects of microfiltration mesh, C-PAM addition and pressure filtration time on coal slime water dehydration were studied. The results showed that the average particle sizes of slime in the primary settling tank, regulating tank and clarifier were 145.1 μm, 103.2 μm and 91.9 μm, respectively. There were particles larger than 830 μm in the primary sedimentation tank and regulating tank. The maximum particle size was larger than 1 200 μm. More than 20% of the particles in the three tanks had a particle size less than 45 μm. The 20 mesh microfiltration and 15 mg /L C-PAM could effectively remove the particulate greater than 830 μm and less than 45 μm, respectively. The two methods together could improve the solid content of mud cake. When the influent suspended solids were less than 3 000 mg/L, the pressure filtration time of slime water in the high-efficiency rapid diaphragm filter press should be more than 40 min. When the influent suspended solids exceeded 5 000 mg/L, the pressure filtration time should be more than 30 min. After treated by the process of microfiltration + mechanical concentration + diaphragm pressure filtration, the solid content of slime cake was more than 70%, and the emission reduction of slime water reached more than 90%.