Enhancing　oxygen　transport　and　reducing　water　flooding　in　the　gas　diffusion　layer　(GDL)　of　proton　exchange　membrane　fuel　cells　are　important　for　improving　cell　performance.　In　this　study,　a　pore-scale　model　based　on　the　lattice　Boltzmann　method　is　proposed,　which　considers　two-phase　flow,　oxygen　diffusion　and　electrochemical　reaction　in　the　GDL.　The　invasion　speed　of　the　water　into　the　GDL　is　determined　by　the　water　generation　rate　and　correspondingly　the　oxygen　consumption　rate.　The　model　is　then　adopted　to　study　effects　of　wettability　and　porosity　distribution　on　the　liquid　water　saturation,　oxygen　concentration　and　current　density.　The　results　demonstrate　that　while　reducing　the　total　saturation　in　the　GDL　is　important,　decreasing　the　local　saturation　near　the　microporous　layer　(MPL)/GDL　interface　is　also　crucial　for　enhancing　cell　performance.　It　is　found　that　GDL　with　locally　enhanced　hydrophobicity　at　the　MPL/GDL　interface　or　gradually　increased　porosity　from　the　GDL　bottom　to　the　GDL　top　can　improve　cell　performance.　Particularly,　by　delicately　designing　the　GDL　porosity,　the　current　density　can　be　considerably　increased　by　201%.　The　developed　pore-scale　model　provides　a　useful　tool　for　understanding　the　underlying　multiphase　reactive　transport　processes　in　GDL　and　designing　the　microscopic　structures　of　GDL.