Metal　foam　flow　field　shows　great　potential　for　next-generation　proton　exchange　membrane　(PEM)　fuel　cell　of　high　power　density　due　to　its　well-connected　pore　structure,　high　thermal　and　electrical　conductivity.　However,　the　complicated　pore　structure　makes　it　a　challenge　for　water　management.　To　tackle　this　issue,　a　novel　design　of　metal　foam　flow　field　with　hierarchical　pore　structure　was　proposed.　Based　on　lattice　Boltzmann　method　(LBM),　the　structure-performance　relationship　between　hierarchical　pore　structure　and　water　discharge　capability　of　flow　field　was　explored　by　using　breakthrough　time.　Furthermore,　an　optimal　hierarchical　pore　structure　for　metal　foam　flow　field　that　shows　superior　water　discharge　capability　was　obtained.　Compared　with　metal　foam　with　uniform　coarse　pore　structure,　breakthrough　time　can　be　reduced　roughly　by　17.6%　in　the　one　with　optimal　hierarchical　pore　structures.　This　finding　provides　a　theoretical　foundation　and　technical　guidance　for　developing　metal　foam　flow　field.