The pore-scale modeling is a powerful tool for increasing our understanding of water transport in the fibrous gas diffusion layer (GDL) of a polymer electrolyte fuel cell (PEFC). In this work, a new dynamic pore-network model for air-water flow in the GDL is developed. It incorporates water vapor transport coupled with liquid water by a phase change model. One important feature of our pore-network model is that a recently developed semi-implicit scheme for the update of water saturation is used. It provides good numerical stability in modeling liquid water transport in the GDL even for very small capillary number values. A number of case studies are conducted to illustrate several important mechanisms of water transport in the GDL, such as cyclic processes of local drainage and imbibition, channeling and capillary-fingering evolutions of water flow pattern, and eruptive water transport. Moreover, we show that liquid water separation in the GDL between the ribs and gas channel (GC) is formed under dry GC condition, which is qualitatively in agreement with in situ experimental results. (C) The Author(s) 2015. Published by ECS. All rights reserved.