Durability is one of the key issues in commercialization of proton exchange membrane fuel cell (PEMFC). The main purpose of this study is to investigate the degradation mechanism of Membrane Electrode Assembly (MEA) based on PTFE/Nafion composite membrane in PEMFC through the MEA/Stack Durability Protocol developed by the Fuel Cell Technical Team (FCTT) of the Freedom CAR and Fuel Partnership. The accelerated life test lasted for 300 h, with voltage decay rate of the MEA about 0.48 mV/h at operating current density 100 mA/cm(2) being achieved. After the acceleration experiment, degradation mechanisms for the MEA based on PTFE/Nafion composite membrane were analyzed in detail by hydrogen-thermal experiment, SEM, TEM, EDS and Ion Chromatographic test. The experimental results show that pinhole formed at outlet position of the composite membrane leads to hydrogen crossover current density exceeding 21 mA/cm(2) at 210 h, with F- and SO42- concentrations sharply increased around 200 h in discharge water of fuel cell from IC results, therefore, membrane failure is the major factor in the failure of MEA. Moreover, the micro-structural damage in the MEA and Pt particles growing up along flow channel even appearing at membrane could be observed from SEM, TEM and EDS results, which play important role in the deterioration of performance and stability for PEMFC. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.