Traditional oxygen evolution reaction (OER) electrocatalysts such as IrO₂ and RuO₂ suffer from high costs and susceptibility to poisoning. Therefore, low-priced, efficient, and stable alternatives urgently need to be developed. In this work, Cu-doped Co metal-organic framework (MOF) was constructed by a one-step solvothermal method, exhibiting excellent OER activity in 1 M KOH with a low overpotential of 235 mV at 10 mA cm⁻² and long-term electrochemical durability for 24 h. The mechanism study showed that the amorphous CoOOH formed by in-situ conversion of MOF structure in the electrochemical water oxidation environment was the real active species. The introduction of Cu significantly changed the morphology and surface electronic structure of Co-MOF-74, facilitated the adsorption of water molecules and accelerated the in-situ conversion of Co₃Cu-MOF-74 to CoOOH, resulting in improved OER performance. Our work provides new insights into the design of efficient OER electrocatalysts and the mechanistic understanding of MOF-derived electrocatalysts.