Metal-decorated　oxide　semiconductors　are　overwhelming　photocatalysts　for　nonoxidative　coupling　of　methane　(NOCM).　However,　the　overall　NOCM　mechanism　remains　an　unopened　black　box,　which　hinders　the　design　of　high-performance　catalysts.　Herein,　we　systematically　studied　a　series　of　noble　metal　(Ag,　Au,　Pt,　Pd,　Cu,　and　Ni)-decorated　oxides　(NaTaO3,　CaTiO3,　LiNbO3,　and　TiO2)　for　NOCM.　We　proposed　that　the　active　sites　for　H　abstraction　and　C-C　coupling　of　CH4　are　spatially　separated.　Specifically,　NaTaO3　only　completes　the　initial　H　abstraction　of　CH4　activation,　while　metal　nanoparticles　are　responsible　for　the　final　C-C　coupling.　Noble　metals　dominate　NOCM　by　significantly　decreasing　the　energy　barrier　of　CH4　dissociation　and　promoting　C-C　coupling.　Among　various　metals,　Ag　is　preferential　for　the　weak　adsorption　of　center　dot　CH3　intermediates　and　subsequent　metal-induced　CC　coupling.　This　contributes　to　Ag/NaTaO3　the　highest　C2H(6)　yield　of　194　mu　mol　g-1　h(-1)　and　stoichiometric　H-2　with　11.2%　quantum　efficiency.　This　work　provides　a　molecular-level　insight　into　the　CH4　coupling　mechanism　on　metal-decorated　photocatalysts.