The　oxygen　spillover　on　the　metal/oxide　electrocatalysts　interface　acts　as　an　essential　role　in　promoting　the　oxygen　evolution　reaction　(OER)　for　proton　exchange　membrane　water　electrolyzers　(PEMWEs).　However,　oxygen　spillover　mechanisms　and　corresponding　regulatory　strategies　are　still　unclear　for　addressing　slow　OH-migration　kinetics.　Herein,　an　interface　is　constructed　between　Iridium　(Ir)　and　Niobium　(Nb)-doped　Titanium　oxide　(TiO2)　with　abundant　oxygen　vacancies　area　by　plasma　processing,　enabling　oxygen　spillover　from　the　metal　Ir　to　supports.　The　optimized　Ir/Nb-doped　TiO2　with　a　significant　OER　activity　(eta　=　253　mV)　and　durability　in　acids　compared　to　commercial　IrO2.　In　situ　experiments　combined　with　theoretical　computations　reveal　the　presence　of　interfacial　oxygen　vacancies　not　only　regulates　the　Ir　structure　toward　boosted　activity　but　also　constructs　a　directional　spillover　pathway　from　Ir　to　interfacial　oxygen　vacancies　area　and　then　TiO2　via　the　OH*-filling　route,　which　strikingly　mitigates　the　OH*　migration　barriers.　In　addition,　the　optimized　Ir/Nb-doped　TiO2　exhibits　excellent　performance　(1.69　V/1.0　A　cm-2@80　degrees　C)　and　long-term　stability　(approximate　to　500　h@1.0　A　cm-2)　with　practical　potential　in　PEMWEs.　This　work　provides　a　unique　insight　into　the　role　of　oxygen　spillover,　paving　the　way　for　designing　Ir-based　catalysts　for　PEMWEs.