A mathematical model of force balance was developed to describe the fluidization characteristics and predict the high-temperature defluidization behavior of iron powders. The calculation was focused on the evolution of the forces acting on particles with temperature based on the surface viscosity and bubble motion. The parameters in the model were obtained by a statistical regression method. Comparing with the experimental data, the simulated results of the defluidization temperature represented a good agreement. This model explained theoretically the dependence of defluidization behavior on the fluidizing gas velocity and gas properties. Accordingly, the stable fluidization and the defluidization regions were determined in the operating phase diagram of fluidization. Crown Copyright (C) 2013 Published by Elsevier B.V. All rights reserved.