The rational design and exploration of the oxygen evolution reaction (OER) electrocatalysts with high efficiency, low cost, and long-term durability are extremely important for overall water splitting. Recently, numerous studies have shown that the OER reaction kinetics can be modified by optimizing components, introducing carbon matrix, and regulating porous nanostructures. Herein, a flexible and controllable electrospinning strategy is proposed to construct porous nitrogen (N)-doped carbon (C) nanofibers (NFs) with nickel-iron (NiFe) alloy nanoparticles encapsulated inside (NiFe@NCNFs) as an OER electrocatalyst. Benefiting from the strong synergistic effects that stem from the one-dimensional mesoporous structures with optimized binary metal components encapsulated in the N-doped carbon nanofibers, the NiFe@NCNFs exhibits enhanced OER performance with a low overpotential (294 mV at 10 mA cm(-2)) and excellent durability (over 10 h at 10 mA cm(-2)) in alkaline solution. Both experimental characterizations and density functional theory (DFT) calculations validate that a suitable binary metal ratio can lead to the optimal catalytic activity. Moreover, a two-electrode electrolyzer is assembled by using NiFe@NCNFs anode and Pt/C cathode in 1.0 M KOH media for the overall water splitting, which delivers an initial cell voltage of only 1.531 V at 10 mA cm(-2), as well as long-term stability up to 20 h. This study sheds light on the design and large-scale production of low-cost and high-performance electrocatalysts toward different energy applications in the future.