An investigation on the reformer operating characteristics for molten carbonate fuel-cell systems has been carried out by using dynamic simulations. A reformer model has been developed to evaluate its capability to provide appropriate gases to fuel-cell stacks under load-following modes. It deals with the interconnected chemical reactions and the heat transfer processes, and the process gas reactions in two separated catalyst beds. The simulation results show: (i) the reformer provides appropriate gases for fuel-cell stacks under stationary conditions, (ii) manipulating the input process gas is effective in controlling the feeding gas to the fuel-cell anode, though there are two side effects (fluctuations of hydrogen concentration and temperature) and (iii) the reformer shows low sensitivity to the disturbances of the flue gas input temperature and the ratio of steam/natural gas, but high sensitivity to the process operating pressure.