This paper reports the results of an investigation into the effects of fabrication techniques on the structure and performance of a gas diffusion layer (GDL) for proton exchange membrane fuel cells (PEMFC). In the experiment, GDLs were fabricated by hot-pressing, carbonization, and graphitization with polyacrylonitrile-based carbon fiber paper as the precursor and phenolic resin as the adhesive to bind the fibers. The effects of the mass fraction of phenolic resin solution on the structure and properties of GDL were investigated. The GDL microstructure was characterized by scanning electron microscopy, mercury intrusion porosimetry, and four-probe method. The structure of GDL was obtained by X-ray tomography, and pore-scale simulations were performed on the structure. The results show that GDL performance can be quantified accurately via experimental characterization and simulations. It is found that for a raw paper impregnated with 15% mass-fraction phenolic resin solution, a GDL with 78% porosity and 30% reduced resistivity can be obtained compared with commercial GDLs.