Metal-organic frameworks (MOFs) have been widely studied as efficient electrocatalysts for water oxida-tion due to their tunable structure and easy preparation.However,the rational design of MOFs-based electrocatalysts and fundamental understanding of their structural evolution during oxygen evolution reaction (OER) remain critical challenges.Here,we report a facile approach to tune the structural trans-formation process of the Co-based zeolitic imidazolate framework (ZIF) during the OER process by using water molecules as a vacancy promoter.The modified ZIF catalyst accelerates the structural transforma-tion from MOF precursor to electrochemical active species and simultaneously enhances the vacancy density during the electrochemical activation process.The optimized electrocatalyst exhibits an extre-mely low overpotential 175 mV to deliver 10 mAcm-2 and superior durability (100 h) at 100 mA cm-2.The comprehensive characterization results reveal the structural transformation from the initial tetrahedral Co sites to cobalt oxyhydroxide (CoOOH) and the formation process of oxygen vacancies (CoOOH-VO) at a high anodic potential.These findings represent a promising way to achieve highly active MOF-based electrocatalysts for water oxidation.