The content of fine mud in the raw coal of coal preparation plant is getting higher and higher with the increase in the mechanization of coal mining. Problems such as poor settlement effect and high overflow concentration often appear when the traditional slime water treatment technology is used to treat high ash and fine coal slurry. As an efficient flocculation method, magnetic flocculation has been widely used in water treatment, but there is less research on the difficult to settle coal slurry water produced by coal preparation plant. Fine coal slurry from a coal preparation plant in Inner Mongolia was used in this study. The effects of magnetite alone and together with polyaluminum chloride and cationic polyacrylamide on the sedimentation characteristics of coal slurry were studied. The stability of the coal slurry system with different magnetite dosages was studied by the Turbiscan analyzer， and the influence of the amount of magnetite powder on the zeta potential of particle surface was studied by Zeta potential analyzer. The results show that when the magnetite is used alone, the turbidity of the supernatant decreases with the increase in magnetite dosages, and then increases, while the sedimentation velocity increases with increasing magnetite dosages, and then decreases. When the magnetite dosage is 48.00 kg/t, the turbidity of the supernatant reaches the lowest value (53.50 NTU), while the sedimentation velocity reaches the maximum value (3.89×10-3 mm/s). When magnetite and PAC is used, the change of the turbidity of supernatant and the sedimentation velocity shows the same trend as the magnetite used alone with the increase of the amount of magnetite powder, and the stability index (ITS) value first increases and then decreases, indicating that with the increase of the amount of magnetite powder, the sedimentation effect of slime water gradually improves. The results of the Turbiscan analyzer shows the coal slurry became steady when excessive magnetite is used, which is not conducive to the settlement of coal slurry. When magnetite, PAC and CPAM are added into coal slurry with the dosages of 10.00 kg/t, 2.00 g/t, and 1.00 g/t, respectively, the initial sedimentation velocity and the turbidity of the supernatant are reached 3.09 mm/s and 64.30 NTU, respectively. The sedimentation effect of the coal slurry improves significantly. The Zeta potential value reduces with the increase of magnetite. The flocs with magnetite as the core are formed by the electrostatic adsorption between the particles and the magnetite in the coal slurry. Moreover, magnetite increases the density and sedimentation velocity of the flocs.