The reduction performance greatly impacts the efficiency of chemical looping hydrogen generation (CLHG) using iron oxides. This work studied the feature of packed bed technology for CLHG. First, a prevention strategy of fuel breakthrough was applied to simulate an industrial process. 25% solid conversion and 2000 mu mol H-2/g Fe2O3 hydrogen production were achieved. Then, a novel idea to directly investigate the reduced particle bed using sub-layers was performed to characterize the reactor. Fe, FeO and Fe3O4 distributed in an orderly manner due to the plug flow gas-solid contact pattern in the reactor. The quantitative calculation showed that the area of Fe3O4 -> FeO took up 80% space of the bed. The kinetic reason for this phenomenon was explored by means of a thermodynamically controlled method. The continuous reduction of iron oxides was successfully decoupled into three independent reactions and the step of Fe3O4 -> FeO was found as the limiting step with a maximum reaction rate of 0.0008 s(-1). Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.