Abstract: The stability and fluidity of dense medium suspension are two contradictory factors that affect the separation performance of dense medium cycloneBy dense medium suspension density and apparent viscosity measurement，the effect of dense medium properties on the separation performance was investigated，and the best coal slime content was determined by labscale dense medium separationThe result showed that coal slime content was the major factor to affect the dense medium stability and fluidityUnder the same dense medium suspension density，higher coal slime content resulted in slower suspension density decline and better dense medium stabilityCoal slime content required for stability of dense medium suspension variedDense medium suspension of higher density could become stable with less coal slime contentThe effect of coal slime content on the fluidity was opposite to that on stabilityHigher suspension density and coal slime content could lead to higher viscosity and fluidity deteriorationIn the labscale dense medium separation，20% of coal slime content was optimal with the lowest mismatch rate acquired in suspension density of 1.50 g/cm3