Abstract: An experimental study is made with the slime samples collected from Linhuan Coal Preparation Plant to explore the effect of hydrophobic modification on dewatering of clean coarse slime. According to both mineral and size analysis of the slime, filter and centrifugal dewatering tests are conducted with the use of four different hydrophobic modification agents − hexadecyl trimethyl ammonium chloride (1631), dodecyl trimethyl ammonium chloride (1231) and self-developed UTG-1 and UTG-2, to analyze the effects that can be produced on promotion of dewatering of slime and the mechanism of action of the modifiers. As revealed by test results, the impurities in the slime are predominately montmorillonite, kaolinite and quartz with a high proportion of fine sizes, which is unfavorable for the dewatering of the slime; filter dewatering of the slime can be favorably promoted by all the modifiers with the UTG-1 being the best in effect as its use at a small dosage of 200 g/t can lead to drastic reduction of moisture of filter cake from 15.83% to less than 8% and increase of filtering rate. And the increase of agitating intensity to a certain extent can help further reduce the cake moisture. Result of centrifugal dewatering test shows that the agent 1631 stands out among the other agents for its best and more stable effect and the ability to help reduce the moisture by a big margin (about 3.61 percentage points). Analysis of mechanisms of action of the agents shows with the use of the modifiers, the coal surface becomes more washer repellent which is helpful to reduction of cake moisture and improvement of dewatering efficiency. The study-derived achievements may serve as a reference for coal preparation plants to improve clean coal dewatering efficiency.