Chemical kinetic models of high-temperature and low-temperature water gas shift reactions (WGSRs) are established in the present study, in accordance with experimental measurements. The reactions are simulated to aid in recognizing the detailed phenomena of the WGSRs. In the developed models, the effects of both the reaction temperature and the steam/CO ratio are taken into account. It is found that the predictions in terms of the conducted models agree with the experimental results very well. When the high-temperature shift reaction (HTSR) and the low-temperature shift reaction (LTSR) in catalyst beds are examined, the CO conversion near the wall is always higher than that along the centerline of the reactor or surrounding it. This is a result of slower velocity or longer residence time of the reactants in the vicinity of the wall. Meanwhile, by virtue of the higher CO concentration at the entrance of the catalyst bed, the intensity of the WGSR is significant nearby and it decays rapidly downstream. When a HTSR and a LTSR are connected together, the CO conversion is nearly completed if the reaction temperature of the LTSR is fixed at 200 degrees C and no matter what temperature of the HTSR is. It follows that a HTSR followed by a LTSR in series is a recommended method in industry for the operation of hydrogen generation. The simulations have provided a detailed and useful insight into the reaction phenomena of the catalytic WGSRs. (C) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.