Abstract: The study is made with the slurry water prepared with the 5^-2 raw coal treated by Qinglongsi Plant as object. Laboratory study is conducted on both natural and flocculation settling of the slurry water to explore its sedimentation characteristics. As evidenced by test result, only through addition of flocculant, can a better clarification result be expected, and the larger the molecular weight of the flocculant, the better the sedimentation effect; the anionic flocculant exhibits a selective flocculation effect for the colloidal coal particles with negative surface charge; only in the case of using flocculant in combination with coagulant, can a high-efficiency and rapid clarification effect be observed; and the combined use of the two agents after the slurry water is diluted to reduce its concentration by half can help accelerate the settling rate and obtain a better clarified supernatant, but increased dosage of flocculant is not only unfavorable to sedimentation effect, but also contrarily retards settling rate of slurry.