Abstract: In order to study the influence of size consist of magnetite powder on separation performance of heavy medium cyclone, pilot-scale test is conducted with a specifically designed heavy medium separation system to explore the results of separation that can be obtained when the medium suspensions used are prepared with magnetite powders containing the <0.045 mm fine sizes of 70%, 80% and 90% respectively. Test result shows that the finer the graded size of magnetite powder, the higher the stability of medium suspension and hence the better the separation result.