Enhancing the surface hydrophobicity of the medium solids is an effective method of increasing gas-solid fluidized bed applicability to dry beneficiation of feed stocks with different external moisture contents. Exploratory experiments determined that stearic acid was appropriate to use as the modifying agent of magnetite powder. Magnetite powder with a hydrophobic surface was prepared with a reagent dosage of 1.5% by wt., a slurry concentration of 15% by wt., a temperature of 60 degrees C and an agitation time of 40 min. The effects of the modification on the fluidization characteristics of the resulting magnetite powder were studied. The results show that modification increases the minimum fluidization velocity but does not apparently change the bed pressure distribution. The uniformity of the bed density is enhanced to a certain degree, indicating an improved fluidization quality. As external moisture of feed-coal increases the fluidization performance of both unmodified and modified magnetite powders decreases gradually. However, when the external moisture content was 4% (the upper limit) the modified magnetite powder still showed good fluidization performance. The upper limit for external moisture content of feed-coal was increased by 100%. (C) 2010 Elsevier B.V. All rights reserved.