Convective flow in the under-rib regions of gas diffusion layers (GDLs) is a non-negligible transport process that can enhance the performance of polymer electrolyte membrane fuel cells (PEMFCs) by facilitating efficient utilization of catalyst layers (CLs) in those regions. The permeability of GDLs has been recognized as a dominant factor influencing the intensity of the under-rib convection in PEMFCs. In this study, the correlation between the permeability of GDLs and the performance of PEMFCs was numerically investigated through a detailed simulation of the transport and electrochemical processes in PEMFCs using a computational fluid dynamics (CFD) tool. Three serpentine flow fields with one, three, or five parallel paths were considered as reactant flow channels for an active cell area of $3;cm{ imes}3;cm$, while the permeability of GDLs was varied from $1{ imes}10^{-12};m^2$ to $1{ imes}10^{-10};m^2$. The effects of the flow field design and the GDL permeability on the performance of PEMFCs were presented, along with their impacts on the local distribution of current density, water content, and reactant concentration.