The N-CoP/CeO2 performs impressive long-term stability for over 42 days@10 mA cm−2 and 21 days@400 mA cm−2. The outstanding catalytic activity and unprecedented long-term durability derived from the robust 3D configuration, the synergetic effect of heterogeneous interfaces, the fast electron transportation, and the optimized absorption/desorption of the oxygen and hydrogen intermediates. Display omitted •The N-CoP/CeO2 is fabricated through hydrothermal and nitridation-phosphorization treatment.•N-CoP/CeO2 possesses excellent conductivity, highly exposed active sites, and fast electron transportation.•N-CoP/CeO2 exhibits remarkable durability at 10 mA cm−2 (>42 days) and 400 mA cm−2 (>21 days) toward water splitting.•The contributions of N-CoP/CeO2 interfaces are deeply analyzed by DFT calculations. Developing high-efficiency, low-cost, and durable bifunctional electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is greatly desirable and challenging. Herein, a highly active and durable nitrogen-doped CoP coupled CeO2 nanowire heterostructure (N-CoP/CeO2) electrocatalyst is prepared on carbon cloth. The resultant N-CoP/CeO2 exhibits superb catalytic activities for OER and HER, featuring low overpotentials of 215 and 74 mV at 10 mA cm−2 in 1.0 M KOH. The N-CoP/CeO2 assembled water electrolyzer has super stability, which needs relatively low cell voltages of 1.52 V@10 mA cm−2 over 42 days (≈95.9 % retention) and 1.80 V@400 mA cm−2 over 21 days (≈94.4 % retention), outperforming most reported cost-effective electrocatalysts. Theoretical calculations reveal that the metallic heterostructure interfaces of N-CoP/CeO2 possess a fast electron transfer pathway, optimized adsorption/desorption process of reactive intermediates, and reduced reaction energetic barriers, thus enhancing the electrocatalytic activity. Additionally, the robust three-dimensional configuration and the oxygen vacancies-rich CeO2 component in N-CoP/CeO2 are regarded as significant contributors to improving stability and promoting long-term durability.