Comprehensive previous studies on electrocatalysts have found that increasing the active area of the catalyst as well as increasing the conductivity are effective methods to enhance the catalytic activity of oxygen evolution reaction (OER). In this work, we hydrothermally synthesized an innovative coral-acicular core-shell heterojunction nanomaterial with an overpotential of ∼150 mV and a Tafel slope of ∼78.6 mV dec−1 at a current density of 10 mA cm−2 by doping appropriate amounts of Fe and coupling g-C3N4. It is found that the specific surface area is 13 times higher than that of precursor Ni0.85Se, and the catalytic performance is increased by 200 %. The heterostructure of this material is demonstrated to improve the electron transport properties through energy band analysis and density functional theory (DFT) simulations, and it is found to have the best theoretical overpotential. The coral-acicular core-shell heterostructure in this work provides a valuable theoretical and practical basis for the design and development of efficient catalysts in terms of morphology and structure. Display omitted •Fe0.09Ni0.76Se@g-C3N4 is a novel coral-acicular core-shell heterojunction structure.•This structure greatly increases the specific surface area of the catalyst.•It is proved by calculation that Fe doping introduces more electrons to react in concert with nickel.•The construction of heterojunction improves the electron transport characteristics.•Fe0.09Ni0.76Se@g-C3N4 only requires an overpotential of 150 mV at 10 mA cm−2.