<p>Hydrogen crossover significantly influences fuel cell performance and can lead to failure. However, developing a three dimensional model to analyze the spatial distribution of extreme hydrogen crossover under varying operating conditions is challenging owing to model complexity and mass transfer mechanisms. This study systematically investigates the effects of various operating conditions on hydrogen crossover distribution using a 25 cm² three-dimensional numerical fuel cell model. The results reveal that increasing the operating relative humidity and temperature enhances hydrogen crossover, thereby altering the membrane water content. Specifically, hydrogen crossover doubles from 6 to 12 A m⁻² as the temperature increases from 50 to 90 °C. Higher inlet pressure increases the dissolved hydrogen concentration, which accelerates hydrogen crossover. Notably, hydrogen crossover increases by ~ 1.86 times from 8 to 15 A m⁻² as the pressure increases from 80/100 to 200/220 kPa. Additionally, operating conditions significantly influence the spatial distribution of hydrogen crossover at different current densities. The difference between the maximum and minimum hydrogen crossover current increases with increasing pressure and temperature. Moreover, the region with strong hydrogen crossover shifts toward the hydrogen inlet and outlet as relative humidity and inlet pressure increase. This study provides insights into the effects of operating conditions on hydrogen permeation using a three-dimensional large-scale model. The findings provide valuable guidance for optimizing fuel cell operations, considering the effects of hydrogen crossover under high temperature and pressure conditions. This approach is crucial for enhancing both cell performance and lifespan.</p>