Abstract: Due to the wide size fraction of coarse slime particles,the phenomenon of entrainment of fine coal in the underflow occurs in the separation process when the Teetered Bed Separator (TBS) is involved. The phenomenon will result in that the clean coal products will be contaminated in the tailings and the lower efficiency of treatment of fine coal particles with chamber press. It is of significance to analyze the motion characteristics of particles with different particle sizes for optimizing the structure of TBS and improving the efficiency of separation. The kinematic characteristics of coarse coal particles with identical density but different sizes during the TBS separation process was analyzed by CFD software FLUENT. For the coarse,middle and fine size fractions,the velocity field,the solution of turbulence kinetic energy and trace lines of particles had been obtained,and the theoretical yields of overflow were calculated,and the verification experiment that had the same parameters with the numerical simulation was conducted. The results show that the extent of trace lines of particles affected by the internal flow field was gradually intensive,and these traces became more chaos with the decrease of particle size. The coarse particle group reported into the underflow in an orderly manner because of the regularity of the velocity field and the turbulent kinetic energy caused by the particle group from the upper part to the bottom of the TBS. The middle particle group shown chaos from in the middle and lower part of the TBS,most of particles of the group reported to the underflow with a minority reporting to the overflow after some repeated movements. The chaos phenomenon occurred in the fine particle group as well,the chaos domain reached to the top part of TBS. The majority of fine particles reported to the overflow,some of them would report to the underflow in the motion of flowing back,the entrainment phenomenon of fine particle happened leading to the losses of some clean coal products. Rationality of choosing the drag law for particles was justified by the consistency between theoretical yield and experimental yield of overflow,i. e. the drag law of non-spherical is suitable for coarse particles and the drag law of spherical is suitable for fine particles. The study shows the weakening effect of particle size by an early accurate size classification,so that the efficiency of TBS could be improved.