Abstract: In order to improve the effect of separation and the adjustment and control means of the slime H. M. cyclone, an external magnetic field is provided through fitting coaxial magnetizing coil on the cylindrical part of the cyclone. It is aimed to study the performance of the cyclone in separation of the < 3 mm coarse-grained slime under the combined effect exerted by the working parameters, such as position, intensity and characteristics of magnetic field, feed inlet pressure, suspension density, and installation angle of cyclone. Test result shows that: application of external magnetic field can lead to improvement of separation performance of the cyclone; in comparison with the conventional method of changing the operating parameters, varying the intensity of magnetic field is a preferred approach for the improvement of separation effect; the law governing the combined effect produced by operating parameters and characteristics of magnetic field is revealed; the potential of applying magnetic field for H. M. cyclone is fully tapped; and a new idea is proposed for making it possible to have varied cyclone operation control strategies and enhance the mechanization and automation level of coal preparation plant.