Water　electrolysis　for　hydrogen　production　holds　great　promise　as　an　energy　conversion　technology.　The　electrolysis　process　contains　two　necessary　electrocatalytic　reactions,　one　is　the　hydrogen　evolution　reaction　(HER)　at　the　cathode,　and　the　other　is　the　oxygen　evolution　reaction　(OER)　at　the　anode.　In　general,　the　kinetics　of　OER　is　much　slower　than　that　of　HER,　dominating　the　overall　of　performance　electrolysis.　As　identified,　the　slow　kinetics　of　catalytic　OER　is　mainly　resulted　from　multiple　electron　transfer　steps,　and　the　catalysts　often　undergo　compositional,　structural,　and　electronic　changes　during　operation,　leading　to　complicated　dynamic　reaction　mechanisms　which　have　not　been　fully　understood.　Obviously,　this　challenge　presents　formidable　obstacles　to　the　development　of　highly　efficient　OER　electrocatalysts.　To　address　the　issue,　it　is　crucial　to　unravel　the　origins　of　intrinsic　OER　activity　and　stability　and　elucidate　the　catalytic　mechanisms　across　diverse　catalyst　materials.　In　this　context,　in-situ/operando　characterization　techniques　would　play　a　pivotal　role　in　understanding　the　catalytic　reaction　mechanisms　by　enabling　real-time　monitoring　of　catalyst　structures　under　operational　conditions.　These　techniques　can　facilitate　the　identification　of　active　sites　for　OER　and　provide　essential　insights　into　the　types　and　quantities　of　key　reaction　intermediates.　This　comprehensive　review　explores　various　catalyst　design　and　synthesis　strategies　aimed　at　enhancing　the　intrinsic　OER　activity　and　stability　of　catalysts　and　examines　the　application　of　advanced　in-situ/operando　techniques　for　probing　catalyst　mechanisms　during　the　OER　process.　Furthermore,　the　imperative　need　for　developing　innovative　in-situ/operando　techniques,　theoretical　artificial　intelligence　and　machine　learning　and　conducting　theoretical　research　to　better　understand　catalyst　structural　evolution　under　conditions　closely　resembling　practical　OER　working　states　is　also　deeply　discussed.　Those　efforts　should　be　able　to　lay　the　foundation　for　the　improved　fabrication　of　practical　OER　catalysts.