An industrial-scale air-dense medium fluidized bed was used to prepare a low-ash coal from a feed coal that was difficult to wash. The low-ash coal provided raw material for preparing low-ash activated carbon. A new fluidized bed density control method for preparing a low-ash coal was proposed, which effectively reduced bed density fluctuation, thus maintaining the uniformity and stability of the bed density. A separation density of 1.42 g=cm3 was maintained in the air-dense medium fluidized bed to produce a clean coal with an ash content of 3.71%, with an EP value of 0.055. Results showed that the air-dense medium fluidized bed system is an efficient dry separation method for difficult-to-wash coal.