In this study, we numerically investigate the effects of CO poisoning on the performance of high-temperature proton exchange membrane fuel cells (HT-PEMFCs) with phosphoric acid (PA)-doped polybenzimidazole (PBI) membranes. A CO poisoning model that rigorously accounts for the adsorption/desorption processes of CO and hydrogen on the anode Pt catalysts and for the subsequent electrochemical oxidation is incorporated into a comprehensive three-dimensional HT-PEMFC model developed in our previous study. The numerical simulations are conducted under different operating temperatures and various percentages of CO in the anode feed stream. The experimental CO poisoning data presented in the literature are used for the model validation study. In particular, a major focus is placed on analyzing the reaction order of the hydrogen adsorption kinetics on the Pt catalyst sites; the reaction order is strongly influenced by the fractional CO coverage on the Pt sites and was mainly assumed to be either first or second order in the previous studies. The simulation results generally agree well with the experimental data, successfully capturing the high poisoning loss at the high current density and/or low operating temperature. The detailed numerical analysis further elucidates the key CO poisoning mechanisms and characteristics in HT-PEMFC at various operating temperatures. Copyright (c) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.