Designing and creating effective, dependable, and conveniently accessible electrocatalysts for the oxygen evolution process is necessary to increase the efficiency of hydrogen production by water electrolysis. In this study, utilizing hydrothermal and electrodeposition methods, we have successfully synthesized a unique 3D Cr-Ni3S2 @NiFe-LDH/NF core-shell p-n heterostructure with a built-in electric field for use as an oxygen evolution reaction (OER) electrocatalyst. By constructing a built-in electric field into the p-n junction, the electronic state of the NiFe-LDH surface can be modified, resulting in an increase in hole concentration and enhanced adsorption of hydroxyl groups from the electrolyte. This facilitates OER reaction kinetics and improves electrocatalytic performance. The Cr-Ni3S2 @NiFe-LDH/NF-120 electrocatalyst exhibits a low overpotential of only 190 mV at a current density of 10 mA cm−2, with a Tafel slope of 33.4 mV dec−1. Remarkably, the overpotential is low, remaining at just 270 mV even at 100 mA cm−2. By operating continuously for 40 h at room temperature in a 1.0 M KOH solution while maintaining a current density of 100 mA cm−2, the exceptional stability was demonstrated. Our research provides a solid framework for the creation of extremely stable and effective 3D core-shell heterojunction electrocatalysts, which can greatly improve OER performance.