•Interfacial mass transfer was accelerated by optimizing gradient porosity.•Water management efficiency was improved by optimizing structural design.•Hydraulic barrier is dominated by the direction of gradient hydrophobicity.•Self-humidifying property bases on balance of hydrophobicity and permeability. Proton exchange membrane fuel cells (PEMFCs) are expected to reveal high adaptability at different operating conditions. One of the key challenges is interfacial water management of microporous layer (MPL) at dry condition. In this paper, MPLs with different structure were prepared for self-humidifying PEMFCs. It was found that when hydrophilic and hydrophobic carbon powder were respectively applied near catalyst layer (CL) and macroporous substrate (MPS), the membrane electrode assembly (MEA) revealed a stable performance at varying humidity condition. When carbon powder employed in the opposite structure, a hydraulic barrier formed at the interface of CL and MPL. These results were demonstrated by a three-dimensional numerical modeling that the intrusion of product water into the hydrophobic pore was decelerated. The gradient-porous MPLs were also prepared to evaluate their practicability at dry condition. Significantly, the MEAs containing gradient-porous MPL revealed a high response on humidity condition. It is attributed that the high pore volume provided more space for gas permeation, and the gradient-porous structure accelerated the water removal. Hence, this work reveals the relation between structural design and performance of MPL at relatively dry conditions. The findings in this study provide a promising strategy for the optimization of self-humidifying PEMFCs. Gradient structural design of microporous layer (MPL) is useful to improve the interfacial water management efficiency of self-humidifying PEMFCs at varying humidity condition. Display omitted