Abstract: In order to further study the effect of high magnetic field intensity on the separation efficiency of coal slime dense medium cyclone, on the basis of previous research results, this paper adopted the method of combining hypothesis, verification and theoretical calculation, and installed hollow cones with different thickness in the column section of the cyclone to qualitatively represent the “accumulation layer” formed under the hypothesis conditions.With the increasing thickness of hollow ring, the ash content of clean coal decreases gradually, and the ash content of tailings remains basically unchanged, that is, the separation accuracy is improved.The results show that there is no magnetite powder deposited with stable thickness in the magnetic field area of the cyclone under the action of high-speed shear of fluid.From the point of force analysis and theoretical derivation, various factors which affecting the formation and destruction magnetic aggregates are fully considered, and the corresponding relationship between the particle size of magnetic aggregates and the parameters such as magnetic field intensity and suspension density are obtained.The results showed that when the magnetic field intensity exceeded a certain value, the particle size of magnetic agglomerate increased significantly, which resulting in poor stability and rheological change of medium suspension, and consequently deteriorating the separation effect of the cyclone.The research results are of great significance for improving the separation theory of composite force field and guiding the magnetic control strategy of slime dense medium cyclone.