The　platinum　single-atom-catalyst　is　verified　as　a　very　successful　route　to　approach　the　size　limit　of　Pt　catalysts,　while　how　to　further　improve　the　catalytic　efficiency　of　Pt　is　a　fundamental　scientific　question　and　is　challenging　because　the　size　issue　of　Pt　is　approached　at　the　ultimate　ceiling　as　single　atoms.　Here,　a　new　route　for　further　improving　Pt　catalytic　efficiency　by　cobalt　(Co)　and　Pt　dual-single-atoms　on　titanium　dioxide　(TiO2　)　surfaces,　which　contains　a　fraction　of　nonbonding　oxygen-coordinated　Co-O-Pt　dimers,　is　reported.　These　Co-Pt　dimer　sites　originate　from　loading　high-density　Pt　single-atoms　and　Co　single-atoms,　with　them　anchoring　randomly　on　the　TiO2　substrate.　This　dual-single-atom　catalyst　yields　13.4%　dimer　sites　and　exhibits　an　ultrahigh　and　stable　photocatalytic　activity　with　a　rate　of　43.467 mmol　g-1　h-1　and　external　quantum　efficiency　of　≈83.4%　at　365 nm.　This　activity　far　exceeds　those　of　equal　amounts　of　Pt　single-atom　and　typical　Pt　clustered　catalysts　by　1.92　and　1.64　times,　respectively.　The　enhancement　mechanism　relies　on　the　oxygen-coordinated　Co-O-Pt　dimer　coupling,　which　can　mutually　optimize　the　electronic　states　of　both　Pt　and　Co　sites　to　weaken　H*　binding.　Namely,　the　＂mute＂　Co　single-atom　is　activated　by　Pt　single-atom　and　the　activity　of　the　Pt　atom　is　further　enhanced　through　the　dimer　interaction.　This　strategy　of　nonbonding　interactive　dimer　sites　and　the　oxygen-mediated　catalytic　mechanisms　provide　emerging　rich　opportunities　for　greatly　improving　the　catalytic　efficiency　and　developing　novel　catalysts　with　creating　new　electronic　states.