Abstract: To clarify the microscopic mechanism of voltage decay caused by nitrogen permeation in proton exchange membrane fuel cells （PEMFCs）operated under anode dead-end mode, molecular dynamics （MD） simulations were performed to investigate the dynamic distribution of nitrogen in perfluorosulfonic acid membranes and its influence on water clusters and hydrogen-bond networks at different hydration levels （λ=3–20）.The simulation results showed that hydrophobic nitrogen molecules disrupted the water-cluster structure and reduced the connectivity of the water network. In the 100 N₂ system, the water-cluster connectivity decreased from 0.38 to 0.24 at λ = 3 and from 0.99 to 0.96 at λ = 20. Meanwhile, the local hydrogen-bond network was weakened, and the number of hydrogen bonds decreased from 1400 to 420 at λ = 3 and from 6035 to 3553 at λ = 20. These results indicate that nitrogen permeation weakens the water network and hydrogen-bond environment required for proton transport in perfluorosulfonic acid membranes, which is an important microscopic mechanism of voltage decay under anode dead-end operation. This work reveals the nitrogen transport mechanism in perfluorosulfonic acid membranes under anode dead-end mode and provides molecular-scale insight for analyzing voltage decay caused by nitrogen accumulation and optimizing anode purge strategies.