The　separation　efficiency　and　recombination　rate　of　photogenerated　electron-hole　pairs　play　a　vital　role　in　photocatalytic　activity.　We　report　the　incorporation　of　ultra-small　subnano　TiOx　clusters　as　outstanding　cocatalysts　on　the　surface　of　plasmonic　Ag/AgCl　to　boost　the　simulated　sunlight　photoreactivity.　The　formed　structure　is　in　favour　of　an　efficient　photoinduced　electron-hole　transfer　process　and　suppressing　the　recombination　rate,　yielding　an　enhanced　photocatalytic　activity.　The　experimental　results　show　that　TiOx@Ag/AgCl　exhibits　an　extraordinarily　high　activity　in　the　photodegradation　of　tetracycline　(TC)　under　simulated　sunlight　irradiation,　which　is　about　21.7　times　higher　than　that　of　bare　Ag/AgCl.　Their　corresponding　apparent　quantum　efficiency　(AQE)　is　up　to　0.917%　at　435　nm　and　17.459%　at　350　nm　during　the　photodegradation　of　TC,　respectively.　Moreover,　TiOx@Ag/AgCl　shows　an　outstanding　long-term　stability　without　obvious　performance　loss　even　after　ten　cycles　of　photodegradation.　The　possible　enhancement　mechanism　of　the　reaction　rate　is　proposed　based　on　the　compositional,　structural,　and　optical　property　analysis.　We　found　that　h(+)　was　the　major　reactive　species　in　the　photodegradation　process　of　TC.　Our　findings　on　ultra-small　TiOx　cocatalysts　would　shed　light　on　the　design　and　development　of　highly　efficient　oxide　cluster　cocatalysts.