Dry coal separation is mainly restricted by the spatial instability in the fluidized bed. Secondary air injection provides a new way to improve the bed stability. In this study, the hydrodynamics and separation operations of the fluidized bed under secondary air injection were investigated using a numerical simulation and experiment. The results show that secondary air injection changed the internal particle circulation mode: the particle flow-field appeared in the middle of the rising stream on both sidewalls, and the sidewall effect was eliminated, thus improving the fluidization quality of the bed. At the appropriate jet velocity (u(j) = 2.4 m/s), the minimum variance of bed density fluctuation was less than 0.127 g/cm(3), further enhancing the bed stability. In addition, 6-50 mm coal was separated in the fluidized bed under secondary air injection. The lowest probable deviation E value was 0.06 g/cm(3), which indicates a good separation performance. (C) 2020 Elsevier B.V. All rights reserved.