Abstract: To guide the fluidized bed industrial application，exploring the ordinary conditions of fine iron ores in the fluidized bed to restore loss of flow between fine iron ore particles.A process with Australia fine iron ore with 61.42% iron is reduced in fluidized bed at the experimental conditions include 923 K to 1 023 K temperatures，particle size range of 0.63 mm to 1.0 mm，coating MgO accounting for 2% of the total quality of fine iron ore，the volume ratio ofcarbon monoxide and H2 and CO monoxide is 4∶1，linear velocity of 0.6 m/s，reduction time is 60 min，and observe the force of fine iron ores in the reduction process.The results show that the particles in the fluidized bed are mainly affected by gas drag force of particles，the bonding force between particles and particles the result of its own gravity.Particle sticking is affected by the external force，which is given by the following formula，when the force is over zero，fine iron ore is in fluidization state；when the force is equal to zero，the fine iron ore is in critical sticking state；and when the force is below zero，fine iron ore is in the defluidization state.Bonding force increases as the solid bridge radius increases at the same temperature and the bonding force between particles is bigger at higher temperature when the radius of solid bridge is the same.Under the experiment conditions，the critical radius of solid bridge is 82~106 nm.

Key words: Fluidized bed, Fluidization, Sticking, Solid bridge