Plasmon-enhanced　photocatalysis　has　attracted　considerable　attention　due　to　its　low　energy　consumption　and　high　energy　throughput.　Surface-enhanced　Raman　scattering　(SERS)　is　a　highly　sensitive　and　label-free　nondestructive　tool　to　investigate　plasmon-driven　photocatalytic　reactions.　Herein,　we　present　a　facile　method　to　fabricate　gap-controlled　Ag　nanoparticle　(NP)　arrays　with　uniform　and　high-density　distribution　of　hot　spots,　which　can　be　employed　as　both　efficient　plasmonic　photocatalysts　and　stable　SERS　platforms.　The　plasmon-driven　catalytic　reaction　of　4-nitrobenzenethiol　(4NBT),　which　transforms　it　into　p,　p＇-dimercaptoazobenzene　(DMAB),　is　detected　by　using　an　in　situ　SERS　technique　at　the　excited　wavelength　of　785　nm.　According　to　the　temperature　and　laser　power　density　dependent　photocatalytic　reaction　rates　observed　on　the　Ag　NP　arrays,　we　quantitatively　determined　that　the　reductive　coupling　of　4NBT　is　more　likely　to　occur　as　the　gap　decreases.　The　finite-difference　time-domain　(FDTD)　simulation　results　demonstrate　that　the　plasmonic　hot　spots　are　significantly　enhanced　with　a　decrease　in　gap,　which　in　turn　reduces　activation　energy.　The　gap-controlled　Ag　NP　arrays　are　efficient　for　both　promotion　and　detection　of　plasmon-driven　catalytic　reactions,　and　may　pave　a　pathway　for　implementing　efficient　plasmonic　photocatalytic　platforms.　(C)　2021　Elsevier　B.V.　All　rights　reserved.