Abstract: In order to explore the influence of size of magnetite powder on stability and viscosity characteristics of heavy-medium suspension, both sedimentation and viscosity tests are conducted with the medium suspension prepared using the <0.045 mm magnetite powder with contents of magnetics of 70%, 80% and 90%. As revealed by test results, when the content of coal slime in suspension remains consistent in all cases, the finer the size of magnetite powder, the higher the stability and viscosity of the suspension; and when viscosity remains unchanged, the finer the size of magnetite powder, the less the amount of coal slime required for preparing the suspension is needed. The test results provide a data basis for realizing rational control of content of coal slime in medium suspension in the case of washing the raw coal with different washability, using different sizes of magnetite powder.