Bubble size distribution is the basic apparent performance and obvious characteristics in the air dense medium fluidized bed (ADMFB). The approaches of numerical simulation and experimental verification were combined to conduct the further research on the bubble generation and movement behavior. The results show that ADMFB could display favorable expanded characteristics after steady fluidization. With different particle size distributions of magnetite powder as medium solids, we selected an appropriate prediction model for the mean bubble diameter in ADMFB. The comparison results indicate that the mean bubble diameters along the bed heights are 35 mm < D_b < 66 mmand 40 mm < D_b < 69 mmwith the magnetite powder of 0.3 mm+0.15 mm and 0.15 mm+0.074 mm, respectively. The prediction model provides good agreements with the experimental and simulation data. Based on the optimal operating gas velocity distribution, the mixture of magnetite powder and <1 mm fine coal as medium solids were utilized to carry out the separation experiment on 6–50 mm raw coal. The results show that an optimal separation density dP of 1.73 g/cm³ with a probable error E of 0.07 g/cm³ and a recovery efficiency of 99.97% is achieved, which indicates good separation performance by applying ADMFB.