The magnetically stabilized fluidized bed has the characteristics of a dispersion gas-solid two-phase flow. The essential condition by which the feedstock was separated by bed density was determined through studying the composition and action of dense medium (gas-solid fluidized bed) on feedstock. The forces exerted on a separated feed with sizes close to the lower limit of separation were analyzed. The correlative formula of the lower limit of separation was obtained theoretically. Experimental results in a 100-mm magnetically fluidized bed model show that the coal can be separated efficiently under a good fluidization state with Ep values of 0.05-0.08. The lower limit of separation is about 0.5 mm. (C) 2003 Elsevier B.V. All rights reserved.