With 03-0.074 mm vanadium-titanium magnetite powder used as the fluidized medium, the overall fluctuation of bed pressure drop and the uniformity and stability of bed density in the secondary air-distribution fluidized bed (SAFB) were experimentally investigated. Compared with the conventional fluidized bed (CFB), SAFB demonstrated smaller fluctuations of bed pressure drop, generated more smaller-sized bubbles, and had a more even bed density, which indicated more stable separation condition. A larger value of (U-mb - U-mf) in SAFB indicates the larger stability region in the bed, which improves the applicability of fluidized bed. To ensure the bed stability within suitable superficial gas velocity U, the operating factors of the secondary air-distribution bed height H-d and the weight fraction of coarse magnetite powder in the mixture of separating medium a should be adjusted to vary in the ranges of 13-17 mm and 80-90%, respectively. With the optimal operation parameters of the static bed height H-s, U, H-d, and alpha, orthogonal array testing technique was adopted to design and perform the separation experiments of 6-25 mm Yiluo coking coal. Finally, the ash and sulfur contents of coal sample were reduced from 38.98% and 131% to 12.26% and 0.82% in SAFB, respectively. The cleaning coal with a yield of 60.74% was obtained at a separating density of 1.64 g/cm(3) and a probable error E-p value of 0.05 g/cm(3). Therefore, SAFB presents better separation efficiency than that of CFB, which indicates a favorable application prospect in industry. (C) 2015 Elsevier B.V. All rights reserved.