Abstract: Based on CFD and separation principle of dense medium cyclone,through analogue stimulation study of flow field inside cyclones under condition of different cone angles,the effect of cone angle on velocity field and pressure field inside cyclone is obtained. With the increase of cone angle,the size of zero axial velocity surface is changed,and then effective separation area of cyclone become bigger,which can increase axial velocity and pressure inside cyclone,improve separation density to prevent coal losing in reject.