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 percent in the one with optimal hierarchical pore structures. This finding provides a theoretical foundation and technical guidance for developing metal foam flow field.