A numerical model has been developed to simulate the parameters distribution in molten carbonate fuel cell (MCFC) stacks under transient conditions. The stack model is the extension of the cell model by taking account of the heat transfer and gas transport processes with regard to the stack configuration. The stack model has been implemented by using a computational-fluid-dynamics (CFD) program. This paper demonstrates the model performance by applying it to calculate the responses of current density and temperature distributions to a step voltage change. The simulated temperature profiles are consistent with the simulated and experimental results from the literature.