A porous material (sponge) was introduced into a typical air dense medium fluidized bed (ADMFB) as an air distribution layer to improve the uniformity and stability in fluidized beds. An ADMFB, an ADMFB with a secondary air distribution plate (PFB), and an ADMFB with a sponge (SFB) were compared by measuring the bed pressure drop and shooting image. Results shows that the introduction of a sponge reduces critical fluidization gas velocity and facilitates high-grade fluidization in beds. A sponge with smaller pores yields better effect on sustaining bed uniformity. In fluidized beds, the trend is that uniform stability is initially promoted and subsequently diminished as the fluidization number N increases. The optimal fluidization is reached when the fluidization number is 1.36. Fluidization quality is improved as the sponge thickness increases. In addition, the findings elucidate the behavior of air bubbles in a bed. The maximum diameter of an air bubble is 4297 cm under the condition that the fluidization number is 136 in an ADMFB with a sponge. (C) 2016 Elsevier B.V. All rights reserved.